Performance Evaluation of IDMA Scheme in Wireless Communication

Table of Contents

Acknowledgements

Synopsis

List of Figures

List of Table

Glossary

1. Introduction
1.1. Development of Wireless Communication Systems
1.2. Multiple Access Schemes
1.2.1. FDMA Scheme
1.2.2. TDMA Scheme
1.2.3. CDMA Scheme
1.3. Motivation
1.4. Problem Statement
1.5. Research Contributions
1.6. Thesis Organization

2. Overview of Interleave-Division Multiple-Access (IDMA) Scheme
2.1. Introduction
2.2. Interleavers in Digital Communication
2.3. Interleavers in IDMA Scheme
2.4. Mechanism of Interleaving Process
2.5. Interleave-Division Multiple-Access (IDMA) Scheme
2.5.1. Comparison of CDMA and IDMA Schemes
2.5.2. IDMA Transmitter and Receiver
2.5.2.1. Basic Primary Signal Estimator (PSE) Function
2.5.2.2. Algorithm for Chip-By-Chip Detection
2.5.2.3. Decoder (DEC) Function
2.5.3. IDMA over Multipath Channels
2.6. Literature Review
2.7. Simulation of IDMA Scheme
2.8. Conclusions

3. Performance Evaluation of Tree Based Interleaver (TBI) in IDMA Scheme
3.1. Introduction
3.2. Motivation
3.3. Mechanism of Tree Based Interleaver (TBI)
3.4. Performance Evaluation of Tree Based Interleaver
3.5. TBI with Unequal Power Allocation Algorithm
3.5.1. Unequal Power Allocation Mechanism
3.5.2. Numerical Results
3.6. Conclusions

4. Performance Evaluation of Tree Based Interleaver in IDMA Scheme with Maximal Ratio Combining (MRC) Diversity
4.1. Introduction
4.2. Diversity Mechanisms
4.2.1. Frequency Diversity
4.2.2. Time Diversity
4.2.3. Space Diversity
4.2.3.1. Transmit Diversity
4.2.3.2. Receive Diversity
4.3. Combining Mechanisms
4.3.1. Selection Combining
4.3.2. Maximal Ratio Combining (MRC)
4.3.3. Equal Gain Combining (EGC)
4.4. Performance Evaluation of IDMA Scheme with MRC Diversity
4.4.1. IDMA Scheme with Maximal Ratio Receiver Combining (MRRC) Diversity
4.4.2. IDMA Scheme with Maximal Ratio Transmitter Combining (MRTC) Diversity
4.5. Simulation Results
4.5.1. Simulation Results of IDMA Scheme using MRRC Diversity
4.5.2. Simulation Results of IDMA Scheme using MRTC Diversity
4.6. Conclusions

5. Correlation Analysis and FPGA Implementation of Interleavers
5.1. Introduction
5.2. Motivation
5.3. Design Criteria for Interleavers in IDMA Scheme
5.4. Correlation in Interleavers
5.5. Correlation Analysis of Interleavers
5.6. Interleaving Mechanism in IDMA Scheme
5.6.1. Random Interleaving (RI) Mechanism
5.6.2. Master Random Interleaving (MRI) Mechanism
5.6.3. Tree Based Interleaving (TBI) Mechanism
5.7. Performance Comparison of Interleavers on FPGA Implementation
5.7.1. Summary of Hardware
5.7.2. Final Register Report
5.7.3. Device Utilization Report
5.7.4. Timing Summary Report
5.8. Conclusions

6. Conclusions
6.1. Suggestions for Further Investigations

References

Appendix

List of Figures

1.1 Progress in wireless communication from 1G to 4G

1.2 Frequency Division Multiple Access (FDMA)

1.3 Time Division Multiple Access (TDMA)

2.1 Mechanism of data interleaving

2.2 CDMA scheme vs. IDMA scheme

2.3 IDMA transmitter and receiver structure

2.4 IDMA transmission in single path

2.5 Flowchart of decoding mechanism in the receiver of IDMA scheme

2.6 IDMA in multipath transmission

2.7 Simulation of IDMA and CDMA schemes

2.8 Simulation of IDMA scheme with Random Interleaver

3.1 Interleaving strategy for Tree Based Interleaving scheme

3.2 Performance of Tree based Interleaver with Random Interleaver

3.3 Comparison of RI, MRI, and TBI for memory requirement

3.4 Comparison of RI, MRI, and TBI for computational complexity at transmitter end

3.5 Comparison of RI, MRI, and TBI for computational complexity at receiver end

3.6 Data formats of RI, MRI, and TBI mechanisms in IDMA scheme

3.7 Simulation of TBI in multi-user environment

3.8 Uncoded IDMA scheme in AWGN and Flat Rayleigh fading environment

3.9 Simulation of RI in coded and uncoded IDMA scheme

3.10 IDMA scheme in uncoded environment for variation in user count

3.11 Simulation of RI in coded and uncoded IDMA scheme

3.12 IDMA scheme in coded environment for variation in user count

3.13 Simulation results for 32 users without coding with RI with various data lengths

3.14 Simulation result for 32 users without coding with TBI with various data lengths

3.15 IDMA scheme in uncoded environment for variation in user count with RI and TBI with unequal power allocation algorithm

3.16 IDMA scheme in rate ½ convolutionally coded environment for variation in user count with RI and TBI with unequal power allocation algorithm

4.1 Frequency diversity Mechanism

4.2 Time Diversity Mechanism

4.3 Transmit diversity with multiple antennas at transmitter side

4.4 Receive Diversity having multiple antennas at receiver side

4.5 Mechanism of Selection combining

4.6 Maximal Ratio Combining (MRC)

4.7 IDMA with MRRC Receiver diversity

4.8 Transmit diversity having two transmitter and one receiver antenna

4.9 Performance of IDMA system with and without MRRC diversity

4.10 Performance of IDMA having Random Interlever with MRRC diversity technque at various iterations count with datalength=1024 spreadlength=16

4.11 Performance comparison at different data length with Random Interleaver with MRRC Diversity

4.12 Performance of IDMA using tree based interleaver with MRRC Diversity

4.13 Simulation of Uncoded IDMA with variation in interleaver

4.14 Performance of Random Interlever with 1Transmitter and 2 Receive Antenna, MRRC diversity Technique

4.15 Performane of master random interleaver with 1Transmitter and 2 Receive Antenna, MRRC diversity Technique

4.16 Performance of Tree based Interleaver With 1Transmitter and 2 Receive Antenna, MRRC diversity Technique

4.17 Perfromance of IDMA scheme with FEC coding with tree based interleaver and datalength=1024 bits

4.18 IDMA scheme with variation in receiver count using MRRC diversity

4.19 Performance of IDMA system using MRTC diversity with random interleaver

4.20 Performance of IDMA at different data lengths using random interleaver with MRTC diversity Scheme

4.21 Uncoded IDMA scheme with variation in datalength for RI & TBI

4.22 Rate ½ Conlutionaly coded IDMA scheme with variation in datalength for RI & TBI

4.23 Rate ½ Conlutionaly coded IDMA scheme with uncoded IDMA scheme

5.1 Mechanism for calculation of resultant user-specific cross-correlation amongst users

5.2 Resultant user-specific cross-correlation for 25 users with RI, MRI,and TBI

5.3 Resultant user-specific cross-correlation for 100 users with RI, MRI, and TBI

5.4 Graphical view of resultant user-specific cross-correlation with RI, MRI,and TBI

5.5 Block Diagram of Random Interleaving Mechanism

5.6 Block Diagram of Master Random Interleaver (MRI)

5.7 Block Diagram of Tree based Interleaving mechanism

List of Tables

3.1 Comparison of Memory requirement of user-specific interleavers in IDMA scheme

3.2 Comparison of Computational complexity of user-specific interleavers/ deinterleavers at transmitter end

3.3 Comparison of Computational complexity of user-specific interleavers/deinterleavers at receiver end

5.1 Peak Resultant User-Specific Cross-Correlation of RI, MRI, and TBI

5.2 Summary of hardware

5.3 Final Register report

5.4 Device utilization report

5.5 Timing summary of interleavers

Glossary

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CHAPTER 1

Introduction

Since the beginning of the 20th century, technologies have placed its marks with stone line for providing new techniques and products for wireless communication. Especially in the past three decades, wireless communication services have penetrated into our society with an explosive growth rate.

Cellular radio was originally developed for offering phone services to mobile subscribers. Now-a-days, it is engaged in even providing a variety of services, including video conferencing, music or movie appreciation, games, internet access. The demands and applications from subscribers stimulate the market and drive the technology for further growth. On the other hand, research and development of communication engineering are undergoing a revolution due to rapid advances in technology.

1.1. Development of Wireless Communication Systems

Wireless cellular communication systems have evolved with the first-generation (1G) of analogue stage using frequency division multiple access (FDMA) scheme. Later, due to rapid advances in technologies based on market demand, it has led to the second-generation (2G) of digital stage with time division multiple access (TDMA) and code division multiple access (CDMA) schemes, and now it has stepped into the third-generation (3G) with eye on fourth-generation (4G) of broadband stage [8, 9, 12].

The most popular technology related to 1G is the Advanced Mobile Phone Service (AMPS) developed in the United States (U.S.) by AT&T in the late 1970s, and later, it was implemented by Ameritech at the end of 1983. The further developed version of AMPS was known as Extended Total Access Communication System (ETACS) developed in Europe in 1985. The both of these systems were employing frequency-division duplex (FDD) and frequency-division multiple-access (FDMA) scheme. Due to problem of slower data rate and lower user base, these analogue systems, soon, were replaced by 2G digital systems based on time-division multiple-access (TDMA) scheme. The representatives of 2G systems i.e. Interim Standard-95 (IS-95) system and the Global System for Mobile Communication (GSM), have been widely deployed throughout the world. The IS-95 system, developed in United States of America, is mainly based on code-division multiple- access (CDMA) scheme while GSM system, developed in Europe, is mainly based on time-division multiple-access (TDMA) scheme.

Due to lots of technological changes and market oriented demands, mobile communication technology has entered in 3G stage. The distinctive features of 3G systems in comparison to 2G systems are inherited with technology of packet- switched high-rate data transmission along with voice services. Specifically, CDMA2000, a representative of 3G systems, builds on the packet-switched technology along with increased data transmission rate, and backward compatibility with original CDMA standards. It is employed primarily in North America and some parts of Asia. Another qualified 3G candidate, wideband CDMA (WCDMA) is referred as an evolution of the GSM technology, including aspects of TDMA and CDMA2000 for global accessibility. The time-division synchronous CDMA (TD- SCDMA) is mainly developed by the Datang Group, China, building on the original CDMA standard to deliver multimedia data, considering its largest user base in its own country. Figure 1.1 demonstrates the development of progress of wireless communication from 1G to 4G, in terms of data rates, with all the technological development observed in meantime. The CDMA and its other extended versions such as IDMA, lie between technological developments from 2G to 3G during the span from 1993 to 2007.

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Figure 1.1: Progress in wireless communication from 1G to 4G¹⁴⁸

Although the standards for further generation systems are still in formative stages, leading companies in the industry have started some groundwork with their researchers. Now-a-days, the techniques related to future wireless communication have become hot topics for research all over the world.

The 3G and beyond systems have been developed to serve people's daily work and life, and to satisfy their demands. The ultimate user needs reliable, cheaper, secure, and low-delay voice & data services anytime and anywhere. The additional features of the future wireless communications include high-speed data and broadband transmission for huge user base, along with global mobility, & scalable quality of service (QoS) for both operators and subscribers.

The above features are imposing technical challenges on system design and stimulate various researches to work on topics related to capacity, complexity and performance of the communication systems [23, 56, 20]. There are also other research topics highly related to the physical layer in wireless systems including optimum channel coding, detection, and diversity mechanisms. For immediate solutions of above problems, near-capacity-achieving forward error correction (FEC) codes are developed to enhance power efficiency while improved detection algorithms are designed to enhance the reliability or bit-error rate (BER) performance. Diversity techniques have been proposed to increase spectral efficiency and diversity for accommodating more users and mitigating fading²⁰. The new horizons on above discussed topics have emerged as “hot cake” for researchers all over the world.

In India, cellular industry came into existence nearly in mid 1990s and since then the average growth rate per annum has been about 85 percent¹. By the end of 2002, the total number of cellular subscribers, in India, had increased to about 10 million subscribers. In addition to it, telecom customers have also been doubled during last two years from 300 million to 600 million. According to Reuters India ³, total mobile users in India, now, stand at 584.32 million, data from the sector regulator showed, behind only China that had 777 million at the end of March 2010.

There is tremendous scope for researches in the area of wireless communication for improving the back-bone of communication systems as per the recommendations of International Telecommunication Union (ITU)⁵. One of the hot-cake areas for research is improvement in technology related to multiple access techniques with communication channels. In the next, section, various multiple access techniques including recently evolved IDMA scheme will be discussed, in brief.

1.2. Multiple Access Schemes

Generally, in wireless communication, large numbers of users are involved in the conversation at a time with each other leading to share the same wireless channel. For sharing of wireless channel, there exist three widely deployed multiple access schemes⁸ popularly known as, frequency-division multiple-access (FDMA), time- division multiple-access (TDMA), and code-division multiple-access (CDMA). It will also be worth mentioning that recently, a new variant of CDMA scheme i.e. interleave-division multiple-access (IDMA) scheme has been proposed⁷⁶.

In the next subsection, the prime multiple access schemes are being presented in brief so as highlight their merits and demerits.

1.2.1. FDMA Scheme:

Frequency Division Multiple Access (FDMA) scheme is reffered as the most common technique employed in analog communication systems utilizing division of entire frequency spectrum into multiple frequencies slots to be assigned to indivdual users, as shown in figure 1.2. With FDMA scheme, each subscriber at any given time is assigned with particular frequency channels for transmission and reception independently. The channel, therefore, is closed to other conversations until the initial call is completed, or handed-off to a different channel. FDMA scheme has been used for first generation analog communication systems.

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Figure 1.2: Frequency Division Multiple Access (FDMA)

The scheme is referred to be inefficient due to underutilization of bandwidth. In addition to it, FDMA systems are bound to employ a guard-band between adjacent channels, for avoiding random Doppler shift, occurring due to the user's random mobility. The guard-bands also reduce the probability of adjacent channels interference, while decrease the spectral efficiency⁹.

1.2.2. TDMA Scheme:

Time Division Multiple Access (TDMA) scheme improves spectrum capacity by splitting each time period into multiple time slots. It allows each user to access the entire radio frequency channel for the allotted time slot of during a call as presented in figure 1.3. Other users are also allowed to share the same frequency channel at different time slots. TDMA scheme is the dominant technology for the second generation (2G) mobile cellular networks.

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Figure 1.3: Time Division Multiple Access (TDMA)

However, the TDMA systems have to be carefully synchronized during communication for all the users to ensure that they are received in the correct time-slots and do not cause the interference to other users⁷. Since it cannot be perfectly controlled in a mobile environment, a guard-time is inserted between each time-slot, which reduces the probability that users will interfere, but decreases the spectral efficiency. Also in case of bursty traffic, user has to wait for his next allotted timeslot which ultimately slows down the data rate during communication⁹.

1.2.3. CDMA Scheme:

Code Division Multiple Access (CDMA) scheme is, basically, based on “spread spectrum” technology. It increases spectrum capacity by allowing all users to occupy all channels at the same time¹⁰. The data streames related to indivual users are spreaded over the whole radio band, and each voice or data call is assigned a unique code to differentiate from the other calls carried over the same spectrum¹⁴. The asynchronous CDMA system offers a key advantage in the flexible allocation of communication resources. It is ideally suited to a mobile network where large numbers of transmitters generating a relatively small amount of traffic at irregular intervals individually.

The performance of CDMA scheme is mainly limited by multiple access interference (MAI) and intersymbol interference (ISI). Its processing gain is reduced considerably with increment in users per sector. The processing gain is referred as a figure of merit in spread spectrum communication. Also, in CDMA scheme, the complexity of decoder increases with increment in user count⁶.

From the viewpoint of sharing communication resources, TDMA scheme is termed to be more efficient to FDMA scheme due to better spectral effinciency while considering the matter of message delay, FDMA scheme outperforms the TDMA scheme. In addition to it, as quoted in⁵ regarding future requirements in wireless communication, it is recommended that a communication system must possess the essential parameters for consumers including low receiver cost, de- centralized control, diversity against fading, power efficiency, multi-media services, high user number, and high throughput along with high spectral efficiency ⁶.

For further way of efficient communication, employing spread spectrum technology, the question regarding alternate way for user separation arises. Recently, a new variant of CDMA scheme known as interleave-division multiple-access (IDMA) scheme has evolved on the horizon of wireless communication [76, 77]. The IDMA scheme employs the interleavers as the only means of user separation in order to ensure privacy related to data of users.

1.3. Motivation

The most commonly employed multiple scheme in the world, i.e. CDMA scheme offers an even better bandwidth-efficiency than TDMA and FDMA schemes, and has been widely adopted in the 3G mobile cellular systems, including CDMA2000, WCDMA, TD-SCDMA systems. It offers robust performance due to its unique feature of processing gain. However, its successful operation is based on rather complex technologies including complex power-control, and multiuser detection techniques, and thus it is comparatively difficult to get implemented, when compared with FDMA and TDMA schemes.

The CDMA mechanism is reported to be unsuitable to support QoS sensitive multimedia traffic. It is extremely difficult to adjust data rate on-a-fly and even the small change in data rate may result with change in processing gain⁷, which further compels to adjust transmitter power. Hence, ultimately rate change for ONE user affects whole cell-wise code-assignment plan ¹⁰. Looking into implementation complexity of CDMA systems, the requirement of very precise power control, powerful multi-user detection, requirement of RAKE receiver, and costly sectorized antennas, becomes highly desirable.

In addition to it, CDMA system needs long frames for signal detection. Therefore, it is well suited for slow-speed continuous-time transmission specially. Apart from it, it inherits poor orthogonality of user-specific spreading codes and merely periodic correlation functions are considered in code design process resulting in poor aperiodic correlations amongst spreading codes for higher user count. Therefore, a big room is left for the researchers, leading to improvement in spreading efficiency of CDMA systems. Apart from it, only unitary codes, i.e., Gold, Walsh, Kasami, etc. have been used in CDMA scheme.

All of the above stated problems come from the same root i.e. inefficient “Unitary codes” i.e. one-code-per-user basis, used for user separation in CDMA systems. Though, the spreading PN-sequences used for user separation in CDMA systems, are orthogonal to each other, but the spreaded data related to all the users may loose its orthogonality, in the channel, in case of high user count. Therefore, the requirement for alternate mechanism for user separation is needed urgently.

In interleaver-division multiple-access (IDMA) scheme, most of above stated problems do not exist due to application of user-specific interleavers as alternate way of user separation in place of unitary spreading PN-sequences used in CDMA scheme. With IDMA scheme, user separation is achieved with the help of user-specific interleavers, having low cross-correlation amongst them⁷⁶.

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