The CDMA (Code Division MulTIple Access) technology, is mulTI-sites connecTIon technology based on the wide frequency communicaTIons. The CDMA multi-sites technology completely adaptes to the high request of modern mobile communications, such as large capacity, high grade, the comprehensive service, the soft cut etc, and it will be the most important develop direction.
This article carries on a description of the CDMA communications system essential elements, pivotal technology and the characteristic, mainly introduces the address choice, the wide frequency system characteristic, the power controlling, the RAKE receiving, the CDMA diversity receiving, the soft cut and so on, it especially disscusses the channel structure and parameter of the Q-CDMA digital cellular mobile communications system wireless channel. Then it carries on a introduction to the simulation tool -SystemView. On this foundation, it has simulated the baseband system of CDMA downlink, the uplink Access Channel and the downlink Traffic Channel, making use of Systemview.It has designed the concrete communications system model.In the model design process, it has given a specific explanation and analysis to the goal of model designning, the concrete structure composition, the simulation flow as well as the simulation results.
KEY WORDS: CDMA, SystemView Simulation, uplink, downlink
table of Contents
Summary II
ABSTRACT III
Chapter 1 Introduction 1
1.1 Background and significance of communication system simulation 1
1.2 Development Overview of CDMA Communication System 1
1.3 The project requirements and the main work arrangement of this article 4
Chapter 2 Selection of CDMA basic theory and development tools 5
2.1 Introduction to CDMA communication system 5
2.1.1 Basic principles of CDMA communication 5
2.1.2 Technical characteristics of CDMA 6
2.1.3 Selection of address code 7
2.2 Key technologies of CDMA communication system 8
2.3 Theoretical basis of the IS-95 CDMA system wireless link 11
2.3.1 Downlink 11
2.3.2 Uplink 13
2.4 Selection of development tools 14
2.5 Brief introduction of Systemview 15
Chapter 3 Simulation Research on CDMA (IS-95) Downlink Traffic Channel 17
3.1 Downlink traffic channel structure 17
3.2 Downlink business channel simulation scheme design and module parameter setting 18
3.3 System debugging and simulation result analysis 20
Chapter 4 Simulation Research on CDMA (IS-95) Uplink Access Channel 23
4.1 Introduction to Uplink Access Channels 23
4.2 Uplink access channel simulation scheme design and module parameter setting 24
4.3 Analysis of system debugging and simulation results 27
Chapter 5 Simulation Research of IS-95 CDMA Downlink Baseband System 30
5.1 Structure of the downlink baseband system 30
5.2 Downlink baseband system simulation scheme design and module parameter setting 31
5.2.1 Sending section 31
5.2.2 Receiving part 32
5.3 System debugging and analysis of simulation results 34
Chapter 6 Conclusion 37
6.1 Summary of project work 37
6.2 Problems and solutions in the design process 38
Acknowledgements 39
References 40
Summary
CDMA (Code Division Multiple Access) technology is a multiple access connection technology based on spread spectrum communication. CDMA multiple access technology is fully suitable for high-performance requirements such as large capacity, high quality, integrated services, and soft handover of modern mobile communication networks. It is an important development direction of modern communication technology.
This article describes the basic principles, characteristics and key technologies of CDMA cellular communication systems in detail. It mainly introduces address code selection, spread spectrum system characteristics, power control, RAKE reception, CDMA diversity reception, soft handover, etc., especially for Q-CDMA The structure, parameters and signal design of the wireless channel of the digital cellular mobile communication system are discussed in detail, and the simulation tool SystemView is introduced. On this basis, the powerful simulation function of SystemView is used to simulate the CDMA downlink baseband system, uplink access channel and downlink service channel establishment module respectively, and a specific communication system model is designed. In the process of model design, specific and detailed explanation and analysis are given for the purpose of model design, specific structural composition, simulation process and simulation results.
Keywords: CDMA, SystemView simulation, uplink, downlink
ABSTRACT
Chapter One Introduction
1.1 Background and Significance of Communication System Simulation In recent decades, the scale and complexity of communication systems have grown at an unprecedented rate, making analysis and design of communication systems cost more time, manpower, and material resources. Existing communication systems are very complicated, mainly reflected in the complex composition of the system, the complicated connections between the modules in the system, and the influence of the external environment on the system is difficult to grasp. This makes system analysis and designers researching the system by mathematical analysis only. The conclusions drawn are often far away from the reality. Sometimes they are limited by the development level of modern mathematics, and even mathematical analysis is impossible.
In this case, there are two options, one is to make the actual system, and the other is to use computer simulation to simulate this system. Obviously, the former is high risk, high cost and long cycle. In contrast, the low-risk, low-cost, high-speed advantages unique to computer simulation will certainly be valued.
Computer simulation of a communication system refers to system analysis and design of mathematical models based on the physical meaning of the modules of the communication system, designers then compile simulation programs based on these models, and use computers to reproduce the operating state of the system to study and analyze system characteristics . The main task of the simulation program of the communication system is to process the "waveform" passed between the modules in the system and analyze the data obtained by the simulation. System analysts need to have a deeper understanding of the various modules (such as modulators and demodulators) that make up the communication system and the relationship between the modules. However, there is a major disadvantage of using computer simulation, that is, its calculation will be quite large. Sometimes even if the fastest computer is used today to execute the simulation program, the running time of the program will be an astronomical number. The amount of calculation is related to the complexity of the system, the choice of simulation model and the simulation method. Obviously, the finer the simulation model, the greater the amount of potential computation [1].
Through computer simulation, we can get a deeper understanding of the performance of the CDMA system, and provide a feasible solution for the final implementation of the CDMA system with better performance in hardware. There are many kinds of communication system simulation tools today, and MATLAB, SystemView, Simulink, etc. are more commonly used. SystemView is a modern communication system design, analysis and simulation test tool that is more suitable for the modeling methods of physical models and mathematical models. In CDMA systems It is often used in simulation [2].
1.2 Overview of the development of CDMA communication systems Since the emergence of cellular communication in the late 1970s, the mobile communication industry around the world has experienced rapid development, and the technology of cellular communication itself has also made great progress. Mobile communication networks have started to simulate cellular The network has developed into a digital cellular network. In terms of multiple access technology, the first-generation analog cellular network used the frequency division multiple access (FDMA) method, which was used in the early 1980s; the time division multiple access (TDMA) system was developed in the late 1980s; after the 1990s, The TDMA digital cellular network represented by GSM has been widely used at home and abroad. In the second half of the 1990s, on the basis of frequency division multiple access (FDMA) and time division multiple access (TDMA) digital cellular networks, code division multiple access (CDMA) cellular network systems, including narrowband and broadband systems, gradually emerged [3 ].
Advocates led by Qualcomm (Qualcomm) of the United States have proposed a system implementation scheme using CDMA technology in cellular mobile communication systems. Through theoretical analysis and continuous field experiments, they proved that this cellular system can fully meet the standards proposed by CTIA (American Cellular Communications Industry Association). The system not only has a large capacity, but also has outstanding advantages such as soft capacity and soft handover. It is considered to be a flexible and advantageous technology for obtaining large capacity and high quality in a mobile communication environment. Since 1998, CDMA commercial systems based on IS-95 have been used in Hong Kong, China, South Korea and other regions and countries, and users have received good feedback. At the 18th meeting of TU TG8 / 1 held in Helsinki, Finland on November 5, 1999, three types (TDMA, CDMA-FDD (frequency division multiplexing), CDMA-TDD (time division multiplexing)) were finally determined. 5 technologies as the basis of the third generation mobile communication, among which WCDMA (Wideband Code Division Multiple Access) in Europe, CDMA 2000 in the United States and TD-SCDMA (Time Division-Sync Code Division Multiple Access) in China are the 3 mainstream standards of 3G [4].
In 1995, after the first CDMA commercial system was in operation, many theoretical advantages of CDMA technology were tested in practice, and they were rapidly promoted and applied in North America, South America, and Asia. Many countries and regions around the world, including Hong Kong, China, South Korea, Japan, and the United States have established CDMA commercial networks. In the United States and Japan, CDMA has become the main domestic mobile communication technology. In the United States, 7 out of 10 mobile communication operating companies choose CDMA. As of April this year, 60% of South Korea's population has become CDMA users. In order to adapt to the rapid development of China's mobile communications market, in April 1999, the State Council approved China Unicom to take charge of the construction, operation and management of China's CDMA network. In September 2000, the National Development Planning Commission and the Ministry of Information Industry issued the "Notice on Matters Related to the Start of CDMA Mobile Communication Network Construction", and China Unicom's CDMA network construction plan was officially launched, thus kicking off the CDMA network construction.
In the second half of 1995, the former Ministry of Posts and Telecommunications and the army decided to use the 800MHz frequency, selected four cities of Beijing, Shanghai, Xi'an, and Guangzhou to establish an CDMA experimental network based on IS-95.
At the end of 1995, the world's first CDMA system based on the IS-95 standard was put into commercial use in Hong Kong. At the end of 1997, four 133CDMA commercial experimental networks in Beijing, Shanghai, Xi'an, and Guangzhou operated by the Great Wall Company of Telecommunications were successively announced, and roaming between networks was realized.
On February 11, 2000, the CDMA mobile switching system independently developed by ZTE successfully docked with Ericsson's CDMA base station system, and basically completed the effectiveness test; CDMA BSS products were launched to the market in the second half of 2000. In January 2001, China Unicom signed a CDMA intellectual property framework agreement with Qualcomm on behalf of the country.
In March 2001, ZTE successfully demonstrated the integrated transmission of voice, data and image services using its independently developed CDMA2000 -1X mobile communication system.This is the first CDMA mobile communication system in China to realize data and image services. It reaches 144K, marking the success of the broadbandization of the domestic CDMA mobile communication system.
On the morning of August 29, 2001, the Ministry of Information Industry held a special meeting to announce the decision of the State Planning Commission. 19 domestic enterprises were approved to be qualified to produce CDMA terminal products. In the afternoon, Hisense Group held a press conference to launch China's first CDMA color screen mobile phone. In addition to green functions such as low radiation, high voice quality, and low power consumption, the phone also has a 256-color color LCD display and a unique 16-harmonic function.
In November 2001, the Fujian Unicom CDMA intelligent network project undertaken by Huawei was opened, and the first prepaid business phone of Unicom's CDMA network was opened. Subsequently, CDMA intelligent networks in Liaoning and Heilongjiang provinces were also opened at the same time. China Telecom has made certain achievements in the field of CDMA2000. The Shenzhen branch opened 2G narrow-band CDMA in 2002. The systems and terminals used are exactly the same as those of Unicom's CDMA network that has not yet been assigned. Unicom will begin to smooth the existing network around 2003. The transition to upgrade to CDMA2000 1x network, which makes mature 3G primary novel services (such as video services, VOD on demand, etc.) already mature in South Korea and Japan and other countries will be introduced in the near future.
So far, some cities have established cdma2000 1X networks, or are transitioning from IS-95 to cdma2000 1X. The total number of CDMA users nationwide has exceeded 7 million by the end of 2002, and by May 2004, more than 20 million.
After the third generation mobile communication (3G) Chinese standard TD-SCDMA became China's communication industry standard on January 20, 2006, in early May 2007, the Ministry of Information Industry promulgated WCDMA proposed by Europe and CDMA2000 proposed by the United States as our communication Industry Standard. This means that China's 3G marketization process has made a substantial breakthrough. TD-SCDMA has always been called the "Chinese standard" of 3G, and WCDMA and CDMA2000 were proposed by Europe and the United States, respectively. China's listing of WCDMA and CDMA2000 as standards in the communications industry means that the Chinese government is fulfilling its commitment to "technical neutrality" to provide a more open and fully competitive market for various communications technologies. It is believed that CDMA will play an increasingly important role in China's future mobile communications market.
In Asia Pacific and North America, the commercialization trend of CDMA technology is most obvious. After 1995, many countries and regions such as South Korea, Japan, Singapore, Australia, Thailand, India, and New Zealand have established CDMA networks. As of the end of December 1999, the total number of CDMA users in the Asia-Pacific region had reached 28 million, and North America had reached 16.5 million. In the United States, seven of the top ten cellular mobile companies use IS-95 CDMA cellular networks, accounting for 70% of the total population. In Europe, where GSM is dominant, CDMA has also received widespread attention from operators. By the end of April 2001, the CDMA network had been put into operation in 35 countries and regions around the world, and the total number of users reached 90 million. South Korea embarked on the development of CDMA technology in 1994. In January 1996, it was the first commercial service for CDMA mobile phones in the world; it began to develop the IMT-2000 test system in 1997. By August 2000, CDMA mobile phone users exceeded 15 million, and the market share The rate was 58%; the CDMA2000 1X test system was successfully developed in September 2000; the CDMA2000 1X commercial service was first launched in the world in October 2000. At present, South Korea has achieved success in the operation of CDMA. Domestic companies have developed their own production system equipment, which has led to the development of the national industry and has a place in the world CDMA stage.
1.3 Subject requirements and main work arrangements of this article This design requirement analyzes the principles, characteristics, and key technologies of the code division multiple access system, that is, the CDMA communication system, discusses the parameters, system structure, and signal design of the CDMA communication system, focusing on mastering channel coding , Address code selection, spreading code characteristics and power control. The SystemView software package is used to simulate the wireless interface of the CDMA system, mainly through the simulation of the CDMA downlink baseband system, the uplink access channel and the downlink traffic channel establishment module. Perform simulation parameter setting and analysis of simulation results.
SystemView is a complete visual development environment for dynamic system design, analysis and simulation [5]. This design scheme uses SystemView software to carry out the simulation of each channel separately by using the CDMA expansion library that comes with the software. By constructing a block diagram of the communication system, a brief introduction to the simulation process, then the module design and parameter configuration, and finally debugging and results analysis.
The thesis is divided into six chapters. The first chapter introduces the CDMA communication system simulation background, requirements and significance, the generation of CDMA technology, and puts forward the main research content and program introduction of this thesis.
The second chapter first introduces the basic principles and main features of the CDMA communication system. Next, the key technologies and link components of the CDMA communication system are described in detail. Finally, the selection of development tools and the introduction of SystemView are discussed.
The third, fourth, and fifth chapters simulate each channel separately. Through the design of the simulation scheme, the configuration of parameters, and the commissioning operation, the results of the simulation operation are analyzed.
Chapter 6 summarizes the work done in this article as a conclusion, and discusses the problems and solutions in the design process and the harvest of this design.
Chapter 2 Selection of CDMA basic theory and development tools
2.1 Introduction of CDMA communication system
2.1.1 Basic principles of CDMA communication
CDMA (Code Division Multiple Ac2cess) technology is a multiple access connection technology based on spread spectrum communication. CDMA multiple access technology is fully suitable for high-performance requirements of modern mobile communication networks such as large capacity, high quality, integrated services, soft handover, and international roaming. With the continuous improvement of CDMA technology and the resolution of some key technologies, the third generation mobile communication system (IMT-2000) based on CDMA multiple access technology has become an important development direction of modern communication technology [6].
CDMA technology distinguishes different users with different orthogonal code sequences, so it is called "code division multiple access" technology. It is a multiple access connection technology based on spread spectrum communication, that is, a high-speed pseudo-random sequence (PN code) with a bandwidth much larger than that of the data signal. Modulate the data signal to be transmitted (spread spectrum), so that the bandwidth of the original data signal is expanded, and then modulated by the carrier and sent out. The receiver uses the exact same pseudo-random PN code to perform correlation processing on the received broadband signal, and converts the broadband signal into a narrow-band signal (de-spread) of the original information data to realize data information communication. The same pseudo-random PN code generated by the receiver must be completely synchronized with the pseudo-random PN code contained in the received signal. Therefore, before transmitting the information signal, a special PN code sequence must be generated (when the sequence is interfered, the receiver still has a high recognition rate), which is used for synchronization, and communication starts after synchronization is established. In a mobile communication system, many mobile stations communicate with other mobile stations through a certain base station at the same time, and the base station distinguishes different mobile stations through multiple access technology.
The technical characteristics of CDMA in mobile communication are: the signals transmitted by each site in the communication network occupy the same bandwidth, the transmission time is arbitrary, and each signal is distinguished by the structural (quasi) orthogonality (code pattern). The basic modulation method is spectrum broadening modulation, and the transmitted modulation signal spectrum is much larger than the information spectrum. Its anti-interference ability is strong. First, the non-spreading interference signal enters the receiver and is multiplied by the spreading code of this station. The interference power is dispersed on the spread spectrum, and the interference power falling on the effective bandwidth is greatly reduced. Secondly, other non-local spreading codes (even the same series of spreading codes) interfere with the receiver, after the relevant acceptance, the output is minimal or no output, only the local spreading code solution completely synchronized to the PN sequence Only output after expansion. Third, when spread spectrum modulation makes the signal bandwidth much larger than the relevant bandwidth, the effect of selective fading caused by multipath is greatly reduced.
2.1.2 Technical characteristics of CDMA In mobile communication systems, the basic types of multiple access methods currently mainly include FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access).
FDMA is to subdivide the limited frequency band into multiple carriers. For example, divide the bandwidth of 890MHz ～ 915MHz according to every 25kHz carrier frequency interval, so that we can get 890.0125MHz, 890.0375MHz, 890.0605MHz ... 1000 carriers. In FDMA, one carrier can only be used by one user at a time. At present, FDMA is mainly used in analog communication systems.
TDMA also subdivides the bandwidth of the system, and at the same time divides each carrier by time slot, which is used by multiple users. For example, GSM (Global System for Mobile Communications) divides carrier waves at 200 KHz frequency intervals, and each carrier is divided into 8 time slots for 8 users. Now our country mainly adopts TDMA GSM system.
In the CDMA system, the signals used by different users to transmit information are not distinguished by different frequencies or different time slots, but by different and unrelated orthogonal codes. From the perspective of frequency domain or time domain, multiple CDMA signals overlap each other. The correlator for the receiver can select a signal in which a predetermined code pattern is used from a plurality of CDMA signals, and a signal using other code patterns cannot be demodulated.
Compared with FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access), CDMA has the following unique advantages.
(1) Large system capacity and high connection rate. In theory, the system capacity of the CDMA mobile network is 20 times larger than that of the analog network and more than 5 times larger than that of GSM. The operation of the CDMA system that has been opened proves that its spectrum utilization rate is about 10 times that of the analog system and about 3 times that of the GSM system. The "processing gain" parameter in the CDMA system is much higher than other systems, plus the CDMA signal occupies the entire frequency band, which is almost 7 times the efficiency of the ordinary narrow-band modulation, so in general, for the same bandwidth, the CDMA system is the capacity of the GSM system 4-5 times, the network congestion is greatly reduced, and the connection rate is naturally high.
(2) Flexible configuration of system capacity. FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access) both have fixed channel allocations that limit system capacity, while CDMA (Code Division Multiple Access) is a broadband transmission that can effectively avoid bandwidth limitations. Although an increase in the number of users is equivalent to an increase in background noise, which will cause a drop in voice quality, there is no limit to the number of users, and operators can consider the trade-off between capacity and voice quality. The same frequency can be used repeatedly in multiple cells. When the number of simultaneous communication sites is reduced, the communication quality is automatically improved, and multiple cells can be automatically balanced according to the amount of traffic and interference.
(3) High voice quality and better system performance quality. The vocoder can dynamically adjust the data transmission rate, and select different levels of transmission according to the appropriate threshold. At the same time, the threshold value can be changed according to the change of background noise. In this way, even in the case of large background noise, you can get better call quality.
(4) Not easy to drop calls. The base station is the guarantee of the mobile phone call. When the user moves to the edge of the coverage of the base station, the base station should automatically "switch" to allow the call to continue, otherwise the call will be dropped. The base station coverage during CDMA system switching is "single coverage, one pair of coverage and one separate coverage", and it is automatically switched to the neighboring relatively free base station, that is, when it is confirmed that the mobile phone has moved to another base station's separate coverage area, Only disconnected from the original base station, so as to ensure that the mobile phone will not be dropped. The CDMA system uses soft handover technology, "connect before disconnect", which completely overcomes the shortcomings of hard handover that is easy to drop calls, and ensures the stability of the call quality during the handover process.
(5) Simple frequency planning. In the CDMA system, users are distinguished by different, unique and specific pseudo-random sequence codes, so different CDMA carriers can be used in adjacent cells. Flexible network planning and simple expansion.
(6) The wireless transmission power is small. Because the CDMA system uses very accurate power control technology and variable rate vocoder, base station equipment and mobile phones and future portable personal communicators can communicate normally with very little transmission power. The transmission power of CDMA mobile phones is usually only 0.6mW, which is nearly a hundred times different from the transmission power of mobile phones of other standards. This means that the service life of mobile phone batteries is extended, smaller batteries can be used, and also, the harm of mobile phone radio waves to the human body is greatly reduced.
(7) The CDMA mobile communication network is a combination of several technologies such as spread spectrum, multiple access, cellular networking and frequency multiplexing.It is a collaborative technology that includes three-dimensional signal processing in the frequency domain, time domain and code domain. . Therefore, it has strong anti-interference, can overcome the selective decay caused by multi-path propagation, improve transmission performance, and has good confidentiality; its ability to overcome co-channel interference is also strong, making all sectors, inter-sector and inter-cell Can be multiplexed with the same frequency to improve spectrum efficiency.
(8) The cost of network construction decreased. Due to the large capacity and high frequency utilization of the CDMA system, it can accommodate more users in a certain frequency band. Due to the characteristics of CDMA technology, under the condition of the same coverage area, the CDMA system needs to build more than 80% fewer base stations than the GSM system, which greatly reduces the cost of network construction [7].
2.1.3 Selection of address codes In the CDMA cellular system, in the selection of address codes, three kinds of codes are adopted [8].
One is a PN code of length 215, which is obtained by adding a "0" after outputting 14 consecutive "0" s of m sequence of length 215-1. It is used to distinguish the signals of different base stations and does not maintain synchronization with the base station, but the phase shift of the PN code sequence used by different base stations is different. The phase shift of each base station's PN code can only be an integer multiple of 64, so 512 values ​​can be used by different base stations. Use different phases of the same sequence as address codes to facilitate searching and synchronization.
The other is a pseudo-random PN sequence with a length of 242-1. It is used for signal security in the downlink, and it is used to distinguish a different mobile station in the uplink. Such a long code is conducive to the security of the signal, and at the same time the base station knows the long code and phase of a particular mobile station, so there is no need to search and acquire it. Uplink channels are distinguished by a long PN code with a period of 242-1, and a common mask associated with the mobile station is used to generate a long code for different users' access channels. Long code PNA and long code provide code division physical channels for access logical channels and uplink service logical channels, respectively. The maximum number of access channels that can be set is n = 32, and the corresponding physical channel is PNAn (n = 1, 2, ..., 32). The maximum settable uplink traffic channel is m = 64, and the corresponding physical channel is PNTm (m = 1, 2, ..., 64). PNAn and PNTm are determined by the 42-bit mask. The uplink includes only two logical channels, namely the access channel and the traffic channel. Their total number of channels (n + m) is equal to 64.
In addition, the CDMA cellular system divides the downlink physical channel into 64 logical channels, that is, a pilot channel and a synchronization channel (which can be changed to a traffic channel if necessary, because the mobile station does not need to monitor the synchronization channel after obtaining synchronization ), 1-7 paging channels (can be changed to traffic channels if necessary) and 55 downlink traffic channels (up to 63). The dividing method is to use Walsh sequence to modulate the signal on the PN sequence. The Walsh sequence generated by the Walsh function is 64 chips. The orthogonal signal has a total of 64 Walsh sequence patterns, denoted as W0, W1, W2, ... W63, which can provide 64 code division channels. The corresponding relationship between logical channels and code division physical channels are: pilot channel W0, synchronization channel W32, paging channel W1-W7 and downlink service information W8-W31, W33-W63. In the service channel, contains service data and Power control sub-channel. The former transmits user information and accompanying signaling information. Due to the orthogonality of Walsh sequences, the signals of different channels are orthogonal, and different mobile station users are distinguished at the same time. Adjacent base stations can use the same Walsh sequence, which may not be orthogonal, but can be distinguished by PN short codes. Since 512 64chips long Walsh sequences are exactly equal to the length of the PN sequence, in the uplink, Walsh sequences are used to perform orthogonal code multi-ary modulation on the signal to improve the quality of the communication link.
2.2 Key technologies of CDMA communication system
1. Power control technology
CDMA uses the same frequency at the same time, and only distinguishes channels by different code words. There are shadows, multipath fading and distance loss effects in the mobile radio environment. The location of cellular mobile stations in the cell is random and often changes, so the path loss varies greatly, especially in multi-cell cellular DS / CDMA systems. , All cells use the same frequency, although in theory, the address codes assigned by different users are orthogonal, but in fact it is difficult to be guaranteed, resulting in the mutual interference of various channels, which will inevitably cause serious multiple access interference , Near-far effect and corner effect.
The CDMA system is to reduce the transmission power, reduce interference, and increase capacity under the premise of ensuring quality. It is a self-interference limiting system that does not require transmit power margin. Power control is a key technology in CDMA. Without good power control, the system cannot achieve the desired goal and cannot form a qualified product. The power control of the CDMA system is divided into downlink power control (that is, controlling the base station transmit power) and reverse power control (that is, controlling the mobile station transmit power), in which reverse power control is particularly important. This is because the channel condition of the reverse link is relatively bad. To ensure the system capacity and communication quality, to overcome the problems of fading and to solve the near-far effect, to a large extent, all rely on reverse power control. Reverse power control includes three types of reverse power control: split-loop power control, closed-loop power control, and outer-loop power control [9].
2. Spread spectrum coding technology
CDMA assigns a unique code sequence (spreading code) to each user and uses it to encode information-bearing signals. The receiver that knows the user of the code sequence decodes the received signal and restores the original data, because the cross-correlation between the user code sequence and other user code sequences is very small. Because the bandwidth of the code sequence is much larger than the bandwidth of the signal carrying the information, the coding process expands the frequency spectrum of the signal, so it is also called spread spectrum modulation, and the resulting signal is also called a spread spectrum signal. CDMA is also usually characterized by spread spectrum multiple access (SSMA). Multiple access capability is given to CDMA for the spread of the transmitted signal spectrum. Therefore, it is very important to understand the generation and performance of spread spectrum signals. Spread spectrum modulation technology must meet two basic requirements:
(1) The bandwidth of the transmitted signal must be much greater than the bandwidth of the information.
(2) The bandwidth of the generated RF signal has nothing to do with the transmitted information.
The receiver uses the same spreading code to perform correlation operations with the received signal to recover the original information it carries. Since the spread spectrum signal expands the frequency spectrum of the signal, it has a series of properties that are different from narrowband signals:
â— Multi-access capability â— Anti-multipath interference capability â— With privacy performance â— Anti-human interference capability â— Low load probability performance â— With narrow-band interference capability
CDMA can be divided into direct sequence spread spectrum (DS) \ frequency hopping spread spectrum (FH) time hopping spread spectrum (TH) and composite spread spectrum according to the different spread spectrum modulation methods it uses, as shown in Figure 2.1.
Figure 2.1 Schematic diagram of CDMA spread spectrum modulation method The composition of the direct sequence spread spectrum (DS-SS) transmitter and receiver is shown in Figure 2.2.
Figure 2.2 Direct sequence spread spectrum (DS-SS) transmitter and receiver structure diagram
3. Soft handover
Due to its unique technical characteristics and the use of RAKE receiver technology, the CDMA system allows mobile stations to maintain communication with two or more cell base stations at the same time, which greatly improves the performance of handover, and only realizes soft handover and softer handover. Distinctive characteristics and technological advancement.
In the IS-95CDMA system, each mobile station has a RAKE receiver with three fingers, which can simultaneously communicate with two or more cell base stations. While communicating with base station A, the mobile station continuously monitors the pilot signal strength of neighboring cells (such as base stations B and C). Whenever the strength of one of the pilots exceeds a predetermined threshold Tadd (such as base station B), it immediately notifies The system commands the base station B to establish communication with the mobile station. At this time, there are signals from two base stations on the downlink. On the reverse link, the mobile switching center (or base station) selects it based on which base station receives the stronger signal, and the time for releasing the weak signal depends on Tdrop and other parameters of Tdrop. When a mobile station in a CDMA system communicates on a service channel, four types of handovers occur: soft handover, softer handover, hard handover, and CDMA to analog handover.
The performance improvement brought by the soft handover comes at the cost of increasing the system complexity, which is mainly manifested in that the mobile station must receive signals from different base stations, which requires a complex RAKE receiver; the base station must maintain communication with it for each The mobile station provides channels, including both the mobile station that is about to switch out of the cell and the mobile station that is switching into the cell; the base station must provide each mobile station that maintains communication with it and is in the inter-cell handover state to the MSC The link is used for reverse link diversity combining to achieve seamless handover, and these mobile stations are not necessarily under the power control of the base station, that is, they do not necessarily belong to the base station. Therefore, the seamless coverage of the system can be achieved by switching, providing high-quality services. In practice, according to the specific requirements of the system, various factors such as system burden, spatial service distribution and wireless propagation environment should be considered comprehensively, and a reasonable and effective switching scheme should be designed [10].
4. Diversity reception Diversity reception technology is to use two or more different methods to receive the same signal to reduce the impact of attenuation, is an effective anti-fading measures. The basic idea is to divide the received signal into multiple independent independent signals, and then combine these signals with different energy according to different rules. Diversity receiving technology can be divided into macrodiversity (macroscopic) and microscopic (microscopic) diversity according to the purpose. According to the signal transmission mode, it can be divided into explicit diversity and implicit diversity. Explicit diversity refers to the transmission method that constitutes the obvious diversity signal, which refers to the diversity of receiving signals using multiple antennas. Implicit diversity refers to the transmission method in which the diversity function is included in the transmission signal. At the receiving end, signal processing technology is used to achieve diversity. It includes interleaving coding technology and frequency hopping technology. Diversity receiving methods mainly include spatial diversity, frequency diversity, polarization diversity and angle diversity.
Spatial diversity: Maintaining sufficient spacing between the two receiving antennas at the receiving end can reduce the correlation between the two received signals.Spatial diversity uses this principle to set up two antennas that maintain a certain distance from each other and connect their respective receiving Machine, and then synthesize the signals of each receiver. Spatial diversity reception can improve the received signal, and can effectively improve the fast fading and smooth channel fading phenomena, thereby greatly reducing the bit error rate of digital signals.
Frequency diversity: At the sending end, using two carrier frequencies that are not in the same relevant bandwidth, the transmitter transmits the same information at the same time; at the receiving end, using two receivers corresponding to different frequencies to receive the two carrying the same information The signal is synthesized after demodulation. Because two carrier frequencies are used, the spectrum utilization rate is reduced.
Polarization diversity: The base station has two different polarization antennas to transmit the same information at the same time, and two different polarization antennas corresponding to the mobile station simultaneously receive two polarization components Ex and Ey containing the same information, using the difference between Ex and Ey Uncorrelated, synthesize it. Since the transmitter power is divided into two antennas, this method halves the transmitter power.
Angle diversity: Two directional antennas are used at the receiving end to point to different directions, so that they receive signals that are independent of each other but contain the same information at different angles, and the received signals are synthesized.è¿™ç§æ–¹æ³•ç”¨äºŽç§»åŠ¨å°æ¯”用于基站å°æ›´åŠ 有效,但这ç§æ–¹æ³•åªé€‚用于10GHz 或更高频率上。
2.3 IS-95 CDMAç³»ç»Ÿæ— çº¿é“¾è·¯çš„ç†è®ºåŸºç¡€
2.3.1 下行链路下行链路采用频分ã€æ‰©é¢‘ç 分ã€æ£äº¤ä¿¡å·å¤šå€æŠ€æœ¯ã€‚
频分区域：å¯é—´éš”1.25MHZ多载波工作，将ä¸åŒé¢‘率的载波指é…ç»™ä¸åŒåŒºåŸŸã€‚
ç 分区域：用一ç§PNç ，ä¾PNç 的相ä½ï¼ˆå移）ä¸åŒåŒºåˆ†ä¸åŒçš„基站站å€ã€‚
ç 分信é“：用æ£äº¤ä¿¡å·åŒºåˆ†ä¿¡é“。
用户识别：以用户掩ç 和长PNç 对用户è¯éŸ³ä¿¡å·å¸§çš„æ•°æ®åŠ 扰。
下行链路的64个信é“是由æ£äº¤çš„Walsh函数æ¥å®žçŽ°ç 分的。而æ¯ä¸ªåŸºç«™çš„下行链路信å·ç”±çŸç PN（215）æ¥è¯†åˆ«çš„。çŸç PNåºåˆ—规定有64个å移，æ¯ä¸€ä¸ªå移为512chips。
下行链路的信é“结构包括导频信é“ã€åŒæ¥ä¿¡é“ã€å¯»å‘¼ä¿¡é“和下行链路业务信é“。这64个下行链路信é“çš„æºä¿¡æ¯åˆ†åˆ«è¢«å„ä¿¡é“对应的ç 片速率为1.2288Mc/sçš„64å…ƒWalsh函数扩展åŽï¼Œç»I/Q支路分别被ç 片速率为1.2288Mc/sçš„çŸç PNåºåˆ—（215）进行四相扩频，然åŽè¿›è¡ŒQPSK调制。
在下行信é“ä¸ï¼ŒåŸºç«™å°è¦åœ¨å¯¼é¢‘ä¿¡é“ä¸æ–地å‘é€å¯¼é¢‘ä¿¡å·ã€‚它是未ç»è°ƒåˆ¶ä¸åŒ…å«ä¿¡æ¯çš„扩频信å·ï¼Œä¸»è¦ç”¨äºŽåŸºç«™è¦†ç›–区内移动å°çš„åŒæ¥æ•èŽ·ã€‚åŒæ¥ä¿¡é“çš„ä¿¡æ¯ç”¨äºŽç§»åŠ¨å°å»ºç«‹ç³»ç»Ÿçš„åŒæ¥ï¼Œå…¶ä¿¡æ¯é€ŸçŽ‡ä¸º1.2kb/s。寻呼信é“以固定的寻呼速率9.6 kb/s或4.8 kb/sä¼ é€ä¿¡æ¯ã€‚在下行业务信é“ä¸ï¼ŒåŸºç«™å°æ˜¯ä»¥å˜é€ŸçŽ‡ä¼ é€ä¿¡æ¯çš„，信æ¯é€ŸçŽ‡å¯ä»¥æ˜¯9.6 kb/sã€4.8 kb/sã€2.4kb/sã€1.2 kb/s，æ¯å¸§æ•°æ®çš„ä¼ é€çŽ‡å¯ä»¥ä¸åŒã€‚尽管是å˜ä¿¡æ¯é€ŸçŽ‡ä¼ é€ï¼Œä½†ç”±äºŽç å…ƒé‡å¤ï¼Œä½¿ç”¨é‡å¤åŽçš„ä¼ è¾“é€ŸçŽ‡ä¿æŒæ’定，为19.2 kb/s。
下行链路业务信é“çš„ä¿¡æºåˆ†åˆ«ä¸º172/80/40/16b/帧（æ¯å¸§20msï¼‰ã€‚æ ¹æ®ç”¨æˆ·è®²è¯æ¿€æ´»ç¨‹åº¦çš„ä¸åŒé€‰å–ä¸åŒçš„速率。当用户ä¸è®²è¯æ—¶ï¼Œé€ŸçŽ‡æœ€ä½Žï¼Œç§»åŠ¨å°çš„å‘射功率也最å°ã€‚速率调整的目的是å‡å°‘相互干扰，增大系统容é‡ã€‚由于是多ç§ä¼ 输速率的信æºï¼Œå½“ä¸åŒæ•°æ®é€ŸçŽ‡æ—¶åˆ©ç”¨é‡ä¼ 次数的ä¸åŒæ¥ä¿è¯è¾ƒä¹‹å‰çš„ç¼–ç 比特率为19.2kb/s。
åŒæ—¶ï¼Œå¯»å‘¼ä¿¡é“和下行业务信é“çš„æ•°æ®æ‰°ç ，长ç 掩盖生æˆç 片速率为1.2288 Mc/sçš„åºåˆ—，没64chips对应1个符å·ï¼Œåˆ™æœ‰ç 速率为1.2288/64=19.2ks/s的扰ç 。寻呼信é“的扰ç 由寻呼长ç 掩盖生æˆï¼Œè€Œä¸‹è¡Œä¸šåŠ¡ä¿¡é“的扰ç 有用户长ç 掩盖生æˆã€‚
下行链路信é“å‚数：
下行链路信é“除引导信é“ä¸ä¼ 输数æ®å¤–，其余信é“çš„å‚数分别如下表2.1-2.3所列，在下行链路ä¸ï¼ŒåŸºç«™å°è¦åœ¨å¯¼é¢‘ä¿¡é“ä¸æ–çš„å‘é€å¯¼é¢‘ä¿¡å·ï¼Œå®ƒæ˜¯æœªç»è°ƒåˆ¶ã€ä¸åŒ…å«ä¿¡æ¯çš„扩频信å·ï¼Œä¸»è¦ç”¨äºŽåŸºç«™è¦†ç›–去内移动å°çš„åŒæ¥æ•èŽ·ã€‚åŒæ¥ä¿¡é“çš„ä¿¡æ¯ç”¨äºŽç§»åŠ¨å°å»ºç«‹ç³»ç»Ÿçš„åŒæ¥ï¼Œå…¶ä¿¡æ¯é€ŸçŽ‡ä¸º1.2kb/s。寻呼信é“以固定的信æ¯é€ŸçŽ‡9600b/s或4800b/sä¼ é€ä¿¡æ¯ã€‚在下行业务信é“，基站å°æ˜¯ä»¥å˜ä¿¡æ¯é€ŸçŽ‡ä¼ é€ä¿¡æ¯çš„，尽管是å˜é€ŸçŽ‡ä¼ é€ï¼Œä½†ç”±äºŽç 符å·çš„é‡å¤ï¼Œä½¿å¾—ä¼ é€çš„调制符å·é€ŸçŽ‡ä¿æŒæ’定，为19.2kb/sã€ï¼‘１】。
表2.1 åŒæ¥ä¿¡é“å‚æ•°æ•°æ®é€ŸçŽ‡ï¼ˆb/s） 1200
PNåç 速率（Mc/s） 1.2288
å·ç§¯ç ç¼–ç 率1/2
ç å…ƒé‡å¤åŽå‡ºçŽ°æ¬¡æ•°2
调制ç 元速率（b/s） 4800
æ¯è°ƒåˆ¶ç 元的åç æ•°256
æ¯æ¯”特的åç æ•°1024
表2.2 寻呼信é“å‚æ•°æ•°æ®é€ŸçŽ‡ï¼ˆb/s） 9600 4800
PNåç 速率（Mc/s） 1.2288 1.2288
å·ç§¯ç ç¼–ç 率1/2 1/2
ç å…ƒé‡å¤åŽå‡ºçŽ°æ¬¡æ•°1 2
调制ç 元速率（b/s） 19200 19200
æ¯è°ƒåˆ¶ç 元的åç æ•°64 64
æ¯æ¯”特的åç æ•°256 256
表2.3 下行链路业务信é“å‚æ•°æ•°æ®é€ŸçŽ‡ï¼ˆb/s） 9600 4800 2400 1200
PNåç 速率（Mc/s） 1.2288 1.2288 1.2288 1.2288
å·ç§¯ç ç¼–ç 率1/2 1/2 1/2 1/2
ç å…ƒé‡å¤åŽå‡ºçŽ°æ¬¡æ•°1 2 4 8
调制ç 元速率（b/s） 19200 19200 19200 19200
æ¯è°ƒåˆ¶ç 元的åç æ•°64 64 64 64
æ¯æ¯”特的åç æ•°128 256 512 1024
2.3.2 上行链路上行链路采用与下行链路相åŒçš„频分ã€æ‰©é¢‘ç 分多å€æŠ€æœ¯ã€‚
频分区域：采用与下行链路相对应的频率ç 分区域：采用与下行链路åŒç›¸ä½çš„PNç ç 分信é“：用ä¸åŒçš„é•¿PNç 进行ç 分信é“，以识别接入信é“和业务信é“用户识别：以用户掩ç 和长PNç 对用户è¯éŸ³ä¿¡å·å¸§çš„æ•°æ®åŠ 扰，以识别用户上行链路CDMAä¿¡é“有上行接入信é“和上行业务信é“组æˆï¼Œå…¶ä¸ä¸Šè¡Œé“¾è·¯æŽ¥å…¥ä¿¡é“çš„æ•°æ®ä¼ 输速率固定为4.8kb/s，由长ç åºåˆ—æ¥è¯†åˆ«ä¸åŒçš„接入信é“，上行链路业务信é“çš„æ•°æ®ä¼ 输速率9.6/4.8/2.4/1.2kb/så¯å˜ï¼Œç”±ç”¨æˆ·é•¿ç æ¥è¯†åˆ«ä¸åŒçš„业务信é“，上行链路的数æ®ä¼ 输帧长为20ms。
上行链路接入信é“çš„ä¿¡æºå¸§ç»“æž„88b/帧，å³æ•°æ®é€ŸçŽ‡ä¸º88/20=4.4kb/s。æ¯å¸§é™„åŠ ä¾›è¯‘ç 用的8ä½å°¾æ¯”ç‰¹ï¼Œåˆ™ä¼ è¾“é€ŸçŽ‡å˜æˆ96/20=4.8kb/s。ç»è¿‡ç¼–ç 率为Ｒï¼ï¼‘/3çš„FECç¼–ç åŽï¼Œä¼ 输速率为4.8kb/s×3=14.4kS/s.ç»è¿‡äºŒé‡ä¼ åŽä¼ 输速率为28.8kS/s.ç»åˆ†ç»„交织处ç†åŽçš„ä¼ è¾“é€ŸçŽ‡ä¸å˜ã€‚交织åŽçš„比特æµæ¯6ä½ç¬¦å·ä¸ºä¸€ç»„，在æ£äº¤è°ƒåˆ¶å™¨è¢«64å…ƒWalsh函数调制，å³æ¯6ä½æ¢æˆ1ä½æŒç»æ—¶é—´çš„Walsh函数åºåˆ—，则其输出信å·çš„Walsh函数符å·çš„ä¼ è¾“é€ŸçŽ‡ä¸º28.8/6=4.8kS/s。æ£äº¤è°ƒåˆ¶å™¨è¾“出的Walsh函数符å·é€ŸçŽ‡ä¸º4.8kS/s，而Walshåºåˆ—çš„ç 片速率为4.8*64=307.2kc/s。调制器输出的åºåˆ—被长ç PNåºåˆ—所掩盖，该PNåºåˆ—ç 片速率为1.2288Mc/s。然åŽI/Q支路分别被ç 片速率为1.2288Mc/sçš„çŸç PN扩展å³QPSK调制。
上行链路信é“å‚数：
表2.4 ä¿¡é“å‚æ•°æ•°æ®é€ŸçŽ‡ï¼ˆb/s） 9600 4800 2400 1200
PNåç 速率（Mc/s） 1.2288 1.2288 1.2288 1.2288
å·ç§¯ç ç¼–ç 率1/3 1/3 1/3 1/3
ä¼ è¾“å 空比100 50 25 12.5
ç 元速率（S/s） 28800 28800 28800 28800
Walsh调制的ç 元数6 6 6 6
Walsh函数符å·é€ŸçŽ‡ï¼ˆS/s） 4800 4800 4800 4800
Walshåç 速率（kc/s） 307.2 307.2 307.2 307.2
调制ç 元宽度208.33 208.33 208.33 208.33
æ¯ç 元的PNåç æ•°42.67 42.67 42.67 42.67
æ¯è°ƒåˆ¶ç 元的PNå—ç æ•°256 256 256 256
æ¯Walshåç çš„PNå—ç æ•°4 4 4 4
表2.5 接入信é“å‚æ•°æ•°æ®é€ŸçŽ‡ï¼ˆb/s） 4800
PNåç 速率（Mc/s） 1.2288
å·ç§¯ç ç¼–ç 率1/3
ç å…ƒé‡å¤åŽå‡ºçŽ°æ¬¡æ•°2
ä¼ è¾“å 空比100
ç 元速率（S/s） 28800
Walsh调制的ç 元数6
Walsh函数符å·é€ŸçŽ‡ï¼ˆS/s） 4800
Walshåç 速率（kc/s） 307.2
调制ç 元宽度208.33
æ¯ç 元的PNåç æ•°42.67
æ¯è°ƒåˆ¶ç 元的PNå—ç æ•°256
æ¯Walshåç çš„PNå—ç æ•°4
2.4 å¼€å‘工具的选择仿真是指通过建立系统的模型æ¥éƒ¨åˆ†æˆ–å…¨éƒ¨åœ°ä»¿çœŸå®žé™…çš„ç³»ç»Ÿï¼Œå¹¶ä¸”å¯¹ç³»ç»Ÿæ¨¡åž‹è¿›è¡Œå®žéªŒç ”ç©¶ï¼Œä»¥æ›¿ä»£å®žé™…ç³»ç»Ÿçš„ç ”ç©¶ã€‚å›½å¤–ä¸å°‘å…¬å¸æŽ¨å‡ºäº†è®¸å¤šä¼˜ç§€çš„仿真软件，其ä¸æ¯”较著å的有:HugesAircraft Companyå¼€å‘çš„SSITD软件(System Simulation in TimeDomain) ,Cadenceå…¬å¸çš„SPW仿真软件包(Signal Process Worksystem),Synopsyså…¬å¸çš„COSSAP仿真软件包和美国Elanixå…¬å¸æŽ¨å‡ºçš„基于PC机Windowså¹³å°çš„SystemView动æ€ç³»ç»Ÿä»¿çœŸè½¯ä»¶ã€‚å…¶ä¸.SystemView动æ€ç³»ç»Ÿä»¿çœŸè½¯ä»¶ä»¥å…¶æ–¹ä¾¿ã€ç›´è§‚ã€å½¢è±¡çš„过程构建系统，æ供丰富的部件资æºï¼Œå¼ºå¤§çš„分æžåŠŸèƒ½å’Œå¯è§†åŒ–开放的体系结构，已é€æ¸è¢«ç”µå工程师ã€ç³»ç»Ÿå¼€å‘/设计人员所认å¯ï¼Œå¹¶ä½œä¸ºå„ç§é€šä¿¡ã€æŽ§åˆ¶åŠå…¶å®ƒç³»ç»Ÿçš„分æžã€è®¾è®¡å’Œä»¿çœŸå¹³å°ä»¥åŠé€šä¿¡ç³»ç»Ÿç»¼åˆå®žéªŒå¹³å°ã€‚
SystemView是一个完整的动æ€ç³»ç»Ÿè®¾è®¡ã€åˆ†æžå’Œä»¿çœŸçš„å¯è§†åŒ–å¼€å‘环境。它å¯ä»¥æž„é€ å„ç§å¤æ‚的模拟ã€æ•°å—ã€æ•°æ¨¡æ··åˆåŠå¤šé€ŸçŽ‡ç³»ç»Ÿï¼Œå¯ç”¨äºŽå„ç§çº¿æ€§ã€éžçº¿æ€§æŽ§åˆ¶ç³»ç»Ÿçš„设计和仿真。
其专业库ä¸çš„IS-95 库ã€3G 库ã€Tu rboCode Library 库ç‰æ›´å……分显示了SystemV iew 用于第三代移动通信系统设计仿真的强大和优越。基于SystemView，的上述优点，我们把SystemView动æ€ä»¿çœŸè½¯ä»¶ä½œä¸ºç 分多å€ç³»ç»Ÿä»¿çœŸçš„首选仿真软件。利用IS-95 (CDMA /PCS) 库和其他专业库的功能模å—, 对CDMA ( IS-95A )通信系统进行仿真, 从而充分展示利用SystemView设计的优越性, 并为以åŽè¿›ä¸€æ¥ç ”究CDMA æ供良好的仿真平å°ã€‚
2.5 Systemview的简å•ä»‹ç»ç¾Žå›½Ellanixå…¬å¸ç³»ç»Ÿä»¿çœŸè½¯ä»¶SystemView是一个完整的动æ€ç³»ç»Ÿè®¾è®¡ã€ä»¿çœŸå’Œåˆ†æžçš„综åˆæ€§å¯è§†åŒ–软件。是一个很好的信å·åŠç³»ç»Ÿåˆ†æžã€è®¾è®¡ã€ç ”究平å°ã€‚它è¿è¡ŒäºŽWindowsæ“作系统有éžå¸¸å‹å¥½çš„ç•Œé¢ï¼Œç”¨æˆ·åªéœ€ç”¨é¼ æ ‡å°±èƒ½å®Œæˆå„ç§å¤æ‚的应用处ç†ï¼Œç”¨æˆ·è¿˜å¯ä»¥é€šè¿‡ç•Œé¢å’Œå¯¹è¯çª—å£å¯¹åŠŸèƒ½æ¨¡å—å‚数进行定义。如定义仿真的起始时间和结æŸæ—¶é—®ï¼Œä»¥åŠç³»ç»Ÿçš„æŠ½æ ·é¢‘çŽ‡ç‰ã€‚使用SystemView能迅速建立和修改系统。对系统进行仿真ã€åˆ†æžå’Œå¤„ç†ï¼Œå¹¶èƒ½åˆ©ç”¨ç³»ç»Ÿæ供的开å‘工具迅速地建立动æ€ç³»ç»Ÿçš„精确模型ã€ï¼‘２】。
SystemView包å«åŸºæœ¬åº“和通信ã€DSPã€é€»è¾‘ã€å°„频ï¼æ¨¡æ‹Ÿã€ç”¨æˆ·ä»£ç ç‰ä¸“业库。
基本库是SyMemViewä»¿çœŸçš„åŸºæœ¬æž„é€ æ¨¡åž‹ã€‚åŸºæœ¬åº“ä¸åŒ…括：信å·æºã€åç³»ç»ŸåŠ æ³•å™¨ã€å系统输入输出端å£ã€ç®—åã€å‡½æ•°ã€ä¹˜æ³•å™¨åŠè§‚察窗ç‰å…±8组基本器件。
通信库：包括了在设计和仿真现代通信系统ä¸å¯èƒ½ç”¨åˆ°çš„å„ç§æ¨¡å—。它使在一å°PC上仿真一个完整的通信系统æˆä¸ºå¯èƒ½ã€‚该库ä¸åŒ…括å„ç§çº é”™ç ç¼–ç ï¼è§£ç 器ã€åŸºå¸¦ä¿¡å·è„‰å†²æˆåž‹å™¨ã€è°ƒåˆ¶å™¨ï¼è§£è°ƒå™¨ã€å„ç§ä¿¡é“模型以åŠæ•°æ®æ¢å¤ç‰æ¨¡å—。
DSP库：包å«å¤§é‡çš„DSP芯片的算法模å¼ä»¿çœŸå’ŒDSP函数，主è¦æœ‰åŠ 法器ã€ä¹˜æ³•å™¨ã€é™¤æ³•å™¨ã€åå‘器ã€å…ˆè¿›å…ˆå‡ºç¼“冲器ã€ç¦»æ•£çš„Hadamardå˜æ¢ã€æ··åˆçš„Radix FFTå˜æ¢ã€FIRå’ŒIIR滤波器ç‰é€»è¾‘库：包括了在设计和仿真数å—电路系统ä¸å¯èƒ½ç”¨åˆ°çš„å„ç§æ¨¡å—。主è¦æœ‰ä¸Žã€æˆ–ã€éžé—¨ã€ç¼“冲器，触å‘器ã€å¯„å˜å™¨ã€è®¡æ•°å™¨ã€å¤šè·¯è°ƒåˆ¶çš„多路输出选择器ã€å¤šè°æŒ¯è¡å™¨ï¼Œæ•°æ¨¡è½¬æ¢å™¨ç‰ã€‚
射频ï¼æ¨¡æ‹Ÿåº“：包括了在设计和仿真高频或模拟电路系统ä¸å¯èƒ½ç”¨åˆ°çš„å„ç§æ¨¡å—，主è¦æœ‰è¿ç®—放大器ã€åŒå¹³è¡¡æ··é¢‘器ã€æ•´æµç”µè·¯ã€é™å¹…器ã€é«˜ä½Žé€šæ»¤æ³¢å™¨é”相环ã€PID调节器ç‰ã€‚
用户代ç 库：å¯ä»¥è®©è®¾è®¡è€…å»ºç«‹è‡ªå·±ä¹ æƒ¯çš„SystemViewå›¾æ ‡åº“ï¼Œè¿™äº›å›¾æ ‡åº“å¯ä»¥ä½¿ç”¨cè¯è¨€ç¼–写并且æ’å…¥æ供的模æ¿ï¼Œå¹¶è‡ªåŠ¨åœ°é›†æˆåˆ°SystemViewä¸ï¼Œè±¡å†…åº“ä¸€æ ·ä½¿ç”¨ã€‚
Also. SystemView还æ供了与Matlab的接å£ï¼Œèƒ½å¾ˆæ–¹ä¾¿åœ°å®žçŽ°ä¸ŽMatlab的交互å¼æ•°æ®ä¼ é€ä¸Žä»¿çœŸã€‚ In short. System Viewæ供了先进快速的设计，仿真环境。ä¸ä»…能设计开å‘创建å系统，而且能方便地建立大的å¤æ‚系统。
ç¬¬ä¸‰ç« CDMA（IS-95）下行链路业务信é“çš„ä»¿çœŸç ”ç©¶
3.1 下行链路业务信é“结构下行链路业务信é“结构如图3.1所示,下行链路业务信é“工作在9600/4800/2400/1200b/sçš„æ•°æ®é€ŸçŽ‡ä¸‹ï¼Œæ ¹æ®ç”¨æˆ·è®²è¯é€Ÿåº¦çš„ä¸åŒé€‰å–ä¸åŒçš„æ•°æ®é€ŸçŽ‡ã€‚业务信é“çš„æ•°æ®åœ¨æ¯å¸§æœ«å°¾å«æœ‰ç¼–ç 器尾比特，å¦å¤–在9.6kb/s å’Œ4.8kb/sçš„æ•°æ®ä¸éƒ½å«æœ‰å¸§è´¨é‡æŒ‡ç¤ºæ¯”特，以帮助接收端判定数æ®é€ŸçŽ‡å’Œè¯¯å¸§çŽ‡ã€‚å› æ¤ï¼Œå®žé™…上下行链路业务信é“çš„ä¿¡æ¯æ¯”特率是8.6/4.0/2.0/0.8kb/s ã€ï¼‘３】。
在下行业务信é“结构ä¸ä¸»è¦åŒ…å«äº†å¸§è´¨é‡æ ‡è®°ã€ç¼–ç 器尾ç ã€å·ç§¯ç¼–ç 器ã€ç¬¦å·é‡å¤ã€å—交织器以åŠæŠ½æ ·å™¨ç‰ã€‚在下行链路业务信é“ä¸ï¼Œæ•°æ®åœ¨ä¼ 输之å‰èµžç»è¿‡ç¼–ç 率为1 / 2 ，约æŸé•¿åº¦ä¸º9çš„å·ç§¯ç¼–ç 。编ç åŽï¼Œå¦‚果数æ®é€ŸçŽ‡ä½ŽäºŽ9 600 b/s，在分组交织以å‰éƒ½è¦é‡å¤ï¼Œä½¿å„ç§ä¿¡æ¯é€ŸçŽ‡å‡å˜æˆç›¸åŒçš„调制ç 元速率，å³19200个调制ç å…ƒæ¯ç§’。é‡å¤ä¹‹åŽè¦è¿›è¡Œåˆ†ç»„交织。 下行链路业务信é“所用的交织跨度ç‰äºŽ20ms ，相当于ç 元速率为19200 S / s时的384 个调制ç 元宽度。交织器组æˆçš„阵列是24 行×l6 列（å³384 个ç 元）。交织åŽçš„æ•™æ®è¦è¿›è¡Œæ•°æ®æ‰°ä¹±ã€‚扰ç 器把交织器和按用户编å€çš„伪éšæœºåºåˆ—PN é•¿ç 进行模2 ç›¸åŠ ã€‚è¿™ç§æ—¶é’Ÿä¸ºl . 2288MHz，长ç ç»åˆ†é¢‘åŽï¼Œç 元速率å˜ä¸º19200S/ s ï¼Œå› è€Œé€å…¥æ¨¡2 åŠ æ³•å™¨è¿›è¡Œæ•°æ®æ‰°ä¹±çš„是æ¯ä¸ªåç ä¸çš„第一个åç 在起作用。下行链路业务信é“æ•°æ®æŽ©ç 使用长ç 的公开掩ç 与上行业务信é“相åŒã€‚在下行链路业务数æ®æ‰°ç 以åŽï¼ŒåŠŸçŽ‡æŽ§åˆ¶æ¯”特æ’入到业务数æ®æµä¸ã€‚
ä¸ºäº†ä½¿ä¸‹è¡Œé“¾è·¯ä¼ è¾“çš„å„ä¿¡é“之间具有æ£äº¤æ€§ï¼Œåœ¨ä¸‹è¡ŒCDMA ä¿¡é“ä¸ä¼ 输的所有信å·éƒ½è¦ç”¨64 元的Walsh 函数进行直åºæ‰©é¢‘æ£äº¤è°ƒåˆ¶ã€‚这是采用BPSK 调制的扩频。 64ä¸ªå‡½æ•°æ ‡å¿—64个ç 分信é“，使下行链路ä¸çš„ç 分信é“相互æ£äº¤ã€‚互ä¸ä¸²æ‰°ã€‚在QPSK 调制å‰ï¼Œè¿˜é¡»ä½¿ç”¨Iå’ŒQ æ£äº¤åºåˆ—对数æ®æµä½œå››ç›¸æ‰©é¢‘调制。然åŽï¼Œç»è¿‡åŸºå¸¦æ»¤æ³¢ï¼Œå¹¶æŒ‰ç…§QPSK æ–¹å¼è¿›è¡Œå‘é€è½½æ³¢è°ƒåˆ¶ã€‚
图3.1 CDMA 下行链路业务信é“结构图
3.2 下行链路业务信é“仿真方案设计åŠæ¨¡å—å‚æ•°è®¾ç½®æ ¹æ®IS-95 下行业务信é“原ç†åŠå…¶ç»“æž„, 用SystemView ä¸çš„模å—进行架构, 系统仿真组æˆå¦‚图3.2所示。系统采用了CDMA /PCS 库ä¸çš„TRFCCH ä¿¡é“模å—, å³ä¸‹è¡Œä¸šåŠ¡ä¿¡é“, 并与通过用其他库ä¸çš„模å—æž„æˆçš„下行业务信é“进行信å·è¾“出比较, 以æ¤è¿›è¡ŒIS-95下行业务信é“的仿真。在仿真开始之å‰,ç³»ç»Ÿçš„æŠ½æ ·é¢‘çŽ‡è®¾ä¸º5MHz。主è¦ç»„æˆæ¨¡å—的设置说明如下：
(1) ä¿¡å·æº(t4, æ¤æ ‡å·ä¸ºä»¿çœŸå›¾ä¸Šå¯¹åº”模å—上的数å—æ ‡å·)
这部分采用了伪éšæœºåºåˆ—PN Seq 模å—, 把信å·å¹…度设为1, 电平数设为2, 频率设为8.6kHz, 作为下行业务信é“ä¿¡æ¯ã€‚
(2) 帧质é‡æ ‡è®°(t18)
采用帧质é‡æ£€æµ‹ç¼–ç 器FrameQ 模å—, 作用是在20msçš„æ•°æ®å¸§åŽé¢åŠ å…¥CRC æ ¡éªŒåŠŸèƒ½çš„ç¼–ç ,这里把数æ®é€ŸçŽ‡è®¾ä¸º8.6kb/s, ä¸ºçš„æ˜¯åœ¨åŠ å…¥12比特/20m s æ ¡éªŒæ¯”ç‰¹å’Œ8比特/20msçš„ç¼–ç 器尾比特åŽ, æ•°æ®é€ŸçŽ‡å˜ä¸º9.6kb/s。
(3) å·ç§¯ç¼–ç 器(t0)
采用å·ç§¯ç¼–ç 器Cnv Coder 模å—, 对输入的ç å…ƒå·ç§¯ç¼–ç , 把输入比特数n, ä¿¡å·ä½k , 约æŸé•¿åº¦l分别设为2, 1, 9, 从而使å·ç§¯ç çš„ç 率为1/ 2。
(4) ç å…ƒé‡å¤(t23)
采用符å·ä¸ç»§å™¨SYMRPT 模å—, 作用是对ç»è¿‡å·ç§¯ç¼–ç åŽ, 在分组交织以å‰çš„å„ç 元进行é‡å¤ã€‚å› ä¸ºåœ¨ä¸‹è¡Œä¸šåŠ¡ä¿¡é“ä¸, åªè¦é€ŸçŽ‡ä½ŽäºŽ9.6kb/s , 在分组交织å‰ç 元都è¦é‡å¤, 从而使å„ç§ä¿¡æ¯é€ŸçŽ‡å˜æˆç›¸åŒçš„调制ç 元速率, å³19.2kb /s。这里在å·ç§¯ç¼–ç åŽæ˜¯19.2kb/s, å› æ¤æŠŠé‡å¤å› å设为1。
(5) å—交织器(t1)
采用交织器Intlvr 模å—, 把数æ®é€ŸçŽ‡è®¾ä¸º19.2kb /s, å› ä¸ºæ˜¯ä¸‹è¡Œä¸šåŠ¡ä¿¡é“, 所以使用24 è¡Œ3 16列å•å…ƒä½œä¸ºäº¤ç»‡é•¿åº¦ã€‚
(6) é•¿ç 扰ç 生æˆ(t15+ t16+ t17)
采用脉冲串PlusTrain 模å—ã€é•¿PN ç LongPn模å—å’Œé‡‡æ ·å™¨Sample 模å—æž„æˆæ•°æ®æ‰°ç , 作用是把交织器输出ç 元和用户的长ç 进行模2åŠ ã€‚è„‰å†²ä¸²çš„é¢‘çŽ‡è®¾ä¸º1. 2288MHz, 幅度设为1, æ ¹æ®æ£å‘业务信é“æ•°æ®æŽ©ç 所使用长ç 的公开掩ç ä¸M 41 到M 32 è¦ç½®æˆâ€ 1100011000″ [1] , 所以长ç PN ç ä¸çš„MaskM 32 to M 39 设为å进制的24,MaskM 40toM 41 设为å进制的3, åŒæ—¶é‡‡æ ·å™¨(t17) çš„é‡‡æ ·é¢‘çŽ‡è®¾ä¸º19.2kHz。
图3.2 下行链路业务信é“仿真组æˆ
(7) å¤ç”¨(t27+ t29)
采用一个功率控制ä½PWR , 功率控制ä½ä¸º800b/s çš„æ•°æ®æµ, 这里由一个伪éšæœºåºåˆ—PN Seq(t28) 产生800b /s çš„æ•°æ®æµã€‚åŒæ—¶é‡‡ç”¨ä¸€ä¸ªç¬¦å·ä¸ç»§æ¨¡å—SYMRPT (t27) , 把é‡å¤å› å设为64, è´Ÿè´£ç å…ƒé‡å¤, 使ç 元速率达到1.2288M b/s。
(8) Walsh 函数生æˆ(t1+ t3+ t12)
采用一个脉冲串PlusTrain 模å—ã€Walsh 函数å‘生器模å—å’Œé‡‡æ ·å™¨Sample 模å—æž„æˆWalsh 函数生æˆå™¨ã€‚脉冲串的幅度设为1, 频率设为1.2288MHz,Walsh 函数å‘生器ä¸Order N 设为64,Row K 设为55, 为了使æ£å‘ä¼ è¾“çš„å„ä¿¡é“之间具有æ£äº¤æ€§, 下行业务信é“ä¸çš„所有信å·éƒ½è¦ç”¨64 阵列的Walsh ç 进行æ£äº¤è°ƒåˆ¶[1]ã€‚é‡‡æ ·å™¨çš„é‡‡æ ·é¢‘çŽ‡è®¾ä¸º1.2288MHz。
(9) Iã€Q ä¿¡é“引导PN åºåˆ—(t11+ t5+ t21)
é‡‡æ ·è„‰å†²ä¸²Plu s Train 模å—å’Œé‡‡æ ·å™¨Sample模å—以åŠI 通é“PN 扩展模å—ã€Q 通é“PN 扩展模å—分别构æˆI ä¿¡é“引导PN åºåˆ—å’ŒQ ä¿¡é“引导PN åºåˆ—ã€‚é‡‡æ ·è„‰å†²çš„å¹…åº¦è®¾ä¸º1, 频率设为1.2288MHz,é‡‡æ ·å™¨é‡‡æ ·é¢‘çŽ‡è®¾ä¸º1.2288MHz。Iã€Q 通é“PN 扩展模å—ä¿æŒåŽŸå®šè®¾ç½®ä¸å˜ã€‚
(10) 调制(t33+ t34+ t19)
利用阶跃函数Step Fct 模å—ã€é‡‡æ ·æ¨¡å—以åŠå¤æ•°æ—‹è½¬æ¨¡å—CxRotate 对ç»è¿‡åŸºå¸¦æ»¤æ³¢å™¨çš„Iã€Q ä¿¡å·è¿›è¡Œè°ƒåˆ¶ã€‚把阶跃函数的幅度设æˆ0, é‡‡æ ·é¢‘çŽ‡è®¾ä¸º4.9152e+ 6Hz, å¤æ•°æ—‹è½¬ä¸çš„相ä½å¢žç›Šè®¾æˆ0, 相ä½å移设为30。
(11) 输出显示(t30+ t31+ t38+ t42)
利用分æžAnalysis 模å—, 查看Iã€Q ä¿¡å·è¾“出, 并进行对比, 在CustmSin Name ä¸è¾“å…¥I_ data å’ŒQ_ data, è¿™æ ·åœ¨è§‚å¯Ÿè¾“å‡ºä¿¡å·æ—¶, 在对应的波形图上方看è§å¯¹åº”çš„ä¿¡å·æ ‡è®°ã€‚
(12) 下行业务信é“利用SystemView 自带的下行业务信é“模å—,å³TRFCCH ä¿¡é“模å—, 利用这个模å—和组建的下行业务信é“进行信å·è¾“出对比。
3.3 系统的调试åŠä»¿çœŸç»“果分æžè¿è¡Œè¯¥ç³»ç»Ÿï¼Œå°†ä¿¡å·ç»è¿‡å•ä¸ªå›¾æ ‡13和组建的å‰å‘业务信é“输出的结果比较，å¯ä»¥çœ‹å‡ºä¸¤ä¸ªä¿¡å·è¾“出基本完全å»åˆï¼Œå¦‚图3.3å’Œ3.4。
图3.3 ä¿¡å·ç»å„å›¾æ ‡ç»„å»ºçš„ä¿¡é“输出波形图3.4 ä¿¡å·ç»å•ä¸ªå›¾æ ‡13的输出波形
为了更好看出两个å‰å‘业务信é“的仿真误差, 把对应的信å·è¾“出进行波形覆盖，在åŒä¸€åæ ‡ç³»ä¸å åŠ , 如图3.5所示。从信å·å åŠ è¾“å‡ºå›¾ä¸, å¯ä»¥å‘现在对应的时间上, ä¿¡å·å¹…度差值很å°, 基本上å¯ä»¥å¿½ç•¥ä¸è®¡ã€‚
图3.5 两个信é“输出信å·å åŠ è¾“å‡º
å› æ¤ï¼Œç”±å›¾æ ‡18åˆ°å›¾æ ‡22组æˆçš„下行业务信é“与å•ä¸ªå›¾æ ‡13的功能相åŒï¼Œç¬¦åˆIS-95CDMAæ ‡å‡†çš„ä¸‹è¡Œé“¾è·¯ä¸šåŠ¡ä¿¡é“模型。
ç¬¬å››ç« CDMA(IS-95)上行链路接入信é“çš„ä»¿çœŸç ”ç©¶
4.1 上行链路接入信é“介ç»ä¸Šè¡Œé“¾è·¯æŽ¥å…¥ä¿¡é“是一个éšæœºæŽ¥å…¥ä¿¡é“，供网内移动å°éšæœºå 用。移动å°åœ¨æ¤ä¿¡é“å‘起呼å«åŠä¼ é€åº”ç”信。 æ¯ä¸ªæŽ¥å…¥ä¿¡é“对应下行链路ä¸çš„一个寻呼信é“，但æ¯ä¸ªå¯»å‘¼ä¿¡é“å¯å¯¹åº”多个接入信é“。移动å°é€šè¿‡æŽ¥å…¥ä¿¡é“å‘基站登记，å‘起呼å«ï¼Œå“应基站å‘æ¥çš„呼å«ç‰ã€‚当呼å«æ—¶ï¼Œåœ¨ç§»åŠ¨å°æ²¡æœ‰è½¬å…¥ä¸šåŠ¡ä¿¡é“以å‰ï¼Œç§»åŠ¨å°é€šè¿‡æŽ¥å…¥ä¿¡é“å‘åŸºç«™ä¼ é€æŽ§åˆ¶ä¿¡æ¯ï¼ˆä¿¡ä»¤ï¼‰ã€‚当需è¦æ—¶ï¼ŒæŽ¥å…¥ä¿¡é“å¯ä»¥å˜æˆä¸šåŠ¡ä¿¡é“ã€‚ç”¨äºŽä¼ è¾“ç”¨æˆ·ä¸šåŠ¡æ•°æ®ã€‚æ‰€ä¼ è¾“çš„æ•°æ®ç»è¿‡ä¸Žç”¨æˆ·å·ç 所对应的长伪éšæœºç çš„å˜æ¢åºåˆ—调制åŽå†ä¼ 输，以使通信ä¿å¯†ã€‚
在一个CDMAä¿¡é“ä¸ï¼Œæœ€å¤šå¯æœ‰32 个接入信é“，最少å¯èƒ½æ˜¯0个。æ¯ä¸ªæŽ¥å…¥ä¿¡é“用ä¸åŒçš„接入信é“长伪éšæœºç åºåˆ—åŠ ä»¥è¯†åˆ«ã€‚ä¸Šè¡Œé“¾è·¯æŽ¥å…¥ä¿¡é“的结构图如图3.6所示,上行链路接入信é“以固定的4.8 kb/s é€ŸçŽ‡ä¼ è¾“ã€‚åœ¨å…¶ä¼ è¾“è¿‡ç¨‹ä¸æ²¡æœ‰éšæœºåŒ–选通门的å‚ä¸Žï¼Œå› è€Œä¸¤ä¸ªé‡å¤çš„ç 符å·å‡è¢«å‘é€ã€‚接入信é“çš„ä¿¡æ¯å¸§é¦–先在æ¯å¸§æœ«å°¾åŠ å…¥8ä½ï¼Œç§°ä¸ºç¼–ç 器尾比特。用于把å·ç§¯ç¼–ç 器å¤ä½åˆ°è§„定的状æ€ï¼Œå·ç§¯ç¼–ç ç¼–ç 率为1ï¼3 ，约æŸé•¿åº¦ä¸º9。å·ç§¯ç¼–译ç çš„åˆå§‹çŠ¶æ€åº”为全0 。以åŽæ¯è¾“å…¥1 个数æ®ç¬¦å·åˆ™äº§ç”Ÿï¼“个编ç 符å·ã€‚在æ¯ä¸ª20ms帧结æŸæ—¶ï¼Œç”±ç¼–ç 器尾比特将其åˆå§‹åŒ–为全ï¼çŠ¶æ€ã€‚接入信é“çš„æ•°æ®é€ŸçŽ‡ä¸º4800b/sï¼Œå› æ¤ï¼Œåœ¨åˆ†ç»„交织å‰ç å…ƒé‡å¤1次，两个é‡å¤çš„ç 元都è¦å‘é€ã€‚ç å…ƒé‡å¤åŽè¦è¿›è¡Œåˆ†ç»„交织。分组交织的跨度为20ms。交织器组æˆçš„阵列是32è¡Œx18列（å³576 个å•å…ƒï¼‰ã€‚输入ç 元（包括é‡å¤å•å…ƒï¼‰æŒ‰é¡ºåºé€åˆ—从左到å³å†™å…¥äº¤ç»‡å™¨ï¼Œè¾“出ç 元则按行从上到下从交织器读出。交织åŽè¿›è¡Œ64进制Walsh函数æ£äº¤è°ƒåˆ¶ã€‚之åŽï¼Œç”¨é•¿ç 进行直接åºåˆ—扩频调制。长ç çš„å„个PNåç 是用一个42ä½çš„掩ç å’Œåºåˆ—产生器的42 ä½çŠ¶æ€çŸ¢é‡è¿›è¡Œæ¨¡2åŠ äº§ç”Ÿçš„ï¼Œåªè¦æ”¹å˜æŽ©ç ，产生的PNåç 的相ä½åˆ™éšä¹‹æ”¹å˜ï¼Œäº§ç”Ÿæ¯ä¸ªç”¨æˆ·ç‰¹å®šçš„掩ç ，并对应一个特定的PN ç 相ä½ã€‚在进行直接åºåˆ—扩频以åŽï¼Œä½¿ç”¨I å’ŒQæ£äº¤åºåˆ—ä½œå››ç›¸æ‰©é¢‘è°ƒåˆ¶ï¼ŒåŠ å…¥åŸºç«™ç‰¹å¾ï¼Œä½¿ç”¨æˆ·ä¿¡å·çš„相ä½å……分地éšæœºåŒ–。这一对I å’ŒQæ£äº¤åºåˆ—称为引导PN åºåˆ—，å³æ£äº¤PNåºåˆ—对。上行链路信é“四相扩频使用的都是固定零å置的PN åºåˆ—对。ç»PN åºåˆ—对扩频生æˆçš„æ£äº¤ä¿¡é“åºåˆ—最åŽè¿›è¡ŒOQPSK 调制。 Q支路的åºåˆ—ç»å»¶è¿Ÿ106.901nsåŽï¼ŒI路和Qè·¯åºåˆ—é€åˆ°åŸºå¸¦æ»¤æ³¢å™¨é™å¸¦å¹¶æ»¤æ³¢ã€‚最åŽæŒ‰QPSK çš„æ–¹å¼è¿›è¡Œå‘é€è½½æ³¢è°ƒåˆ¶ã€‚
图3.6 上行链路接入信é“结构
4.2 上行链路接入信é“仿真方案设计åŠæ¨¡å—å‚æ•°è®¾ç½®æ ¹æ®IS-95 上行链路接入信é“原ç†åŠå…¶ç»“æž„, 用SystemView ä¸çš„模å—进行仿真, 系统仿真组æˆå¦‚图3.7所示。系统采用了CDMA /PCS 库ä¸çš„AccessCHä¿¡é“模å—, å³ä¸Šè¡Œé“¾è·¯æŽ¥å…¥ä¿¡é“, 并与通过用其他库ä¸çš„模å—æž„æˆçš„上行链路接入信é“进行信å·è¾“出比较, 以æ¤è¿›è¡ŒIS-95上行链路接入信é“的仿真。在仿真开始之å‰,ç³»ç»Ÿçš„æŠ½æ ·é¢‘çŽ‡è®¾ä¸º5MHzï¼Œé‡‡æ ·ç‚¹æ•°ä¸º5000个。
图ä¸å›¾æ ‡l 是AccessCHä¿¡é“模å—其功能也å¯ç”±CDMA库ã€é€šä¿¡åº“以åŠä¸€äº›ç›¸å…³å›¾æ ‡ç»„æˆçš„系统æ¥å®Œæˆã€‚图ä¸ä»¥ä¼ªéšæœºåºåˆ—å‘ç”Ÿå™¨å›¾æ ‡0作为系统的信æ¯æºã€‚它产生的åºåˆ—分为两路，分别ç»è¿‡ç”±å›¾æ ‡3ã€4 åˆ°å›¾æ ‡33 ç‰ç»„æˆçš„ä¿¡å·é€šè·¯å’Œå›¾æ ‡1。为了é™ä½Žç³»ç»Ÿçš„最高信å·é¢‘率以æ高仿真效率，两路信é“å‡æœªè¿›è¡Œè½½æ³¢è°ƒåˆ¶ï¼Œè€Œä¸»è¦é’ˆå¯¹å‰é¢æ‰€è¿°å„基带信å·å¤„ç†æ¥éª¤è¿›è¡Œä»¿çœŸã€‚
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CL-2H Copper Connecting Terminals
Our company specializes in the production and sales of all kinds of terminals, copper terminals, nose wire ears, cold pressed terminals, copper joints, but also according to customer requirements for customization and production, our raw materials are produced and sold by ourselves, we have their own raw materials processing plant, high purity T2 copper, quality and quantity, come to me to order it!
CL-2H Copper Connecting Terminals
Taixing Longyi Terminals Co.,Ltd. , https://www.txlyterminals.com