Performance Mimo Cdma Harq 64 Qam

PERFORMANCE ANALYSIS IN MIMO CDMA SYSTEM WITH MODIFIED HYBRID-ARQ AND 64 QAM

T. Yasodha Associate Professor, Department of ECE

Christian College of Engineering and Technology Oddanchatram, Tamil Nadu, India-624619

Email: [email protected] ______________________________________________________________________________ Abstract In the emerging era of 4G wireless technologies, Multiple Input-Multiple Output systems with hybrid automatic – repeat – request (HARQ) promises high throughput with high reliability. Hybrid ARQ, an extension of ARQ that incorporates forward error correction coding, is a retransmission scheme employed in current communications systems. The use of HARQ can contribute to efficient utilization of the available resources and the provision of reliable services in latest-generation systems. This paper focuses on wireless system of multiple-input multiple-output (MIMO) design using HARQ. MIMO-HARQ offers new opportunities because of the additional degrees of freedom introduced by the multiple antennas at the transmitter and receiver as well as less erroneous channel in case of poor channel conditions. In this paper, the performance of MIMO CDMA system is compared using Hybrid Acknowledgement Repeat Request (HARQ) and 64 bit Quadrature Amplitude Modulation (64-QAM) and the simulation is carried on using the SPARTAN-3 kit. Keywords: MIMO, CDMA, HARQ, QAM, AWGN ______________________________________________________________________________ 1. INTRODUCTION

Wireless mobile communication is one of the fastest growing markets worldwide. The main reasons for these are reduction in the service cost and user equipment cost. The evolution of new systems require better quality of service (QoS), higher data rates and the need to support the growing number of users. MIMO is a promising technology, which helps to meet requirements of the future Broadband Wireless Access systems. It provides increased spectral efficiency through spatial multiplexing and better link reliability through antenna diversity. Multiple antennas provide additional degrees of freedom, leading to significant capacity increase. Multiple antennas also provide beam forming gains and reduce the outage probability. The success of the wireless systems always depends on the data rate or network capacity. Radio spectrum is a limited and costly resource. The number of users and the bandwidth requirements of users are increasing rapidly. So the spectrum has to be used efficiently. The MIMO systems are expected to support high band width required services like high definition video transmission in future. In spatial multiplexing MIMO there will be multiple antennas at the transmitter and multiple receive antennas which receive the signal and decodes the individual streams those had mixed up in the channel. MIMO systems are subjected to inter stream interference. When the interference is high, transmission may be severely affected even when the received power per antenna is large.

Automatic repeat request (ARQ) protocols are used to improve the reliability of communications networks for overcoming the packet loss and interference. In ARQ, the coding overhead is small, and the system throughput is not considerably affected, when the channel quality is good. But, when the channel deteriorates, the retransmissions may result in significant throughput loss. A possible remedy is to use an error correcting code apart from ARQ in order to provide a more reliable channel which in turn reduces the throughput of the system.

Hybrid ARQ (HARQ) systems attempt to reap the benefits of both ARQ and forward error

T. Yasodha ,G. J. P&A Sc and Tech., 2012v03i3, 12 - 19ISSN: 2249-7188

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correction (FEC) by exploiting the high coding gain of FEC and the rate flexibility of ARQ protocol such that data can be transmitted with a minimum error. In a pure ARQ protocol, a received packet containing error is discarded and the retransmission is requested. In HARQ, earlier received erroneous packets are combined in an intelligent way with the subsequent received packets to improve the decoding reliability. The HARQ receiver handles error detection, correction as well as retransmission requests simultaneously.

We propose and evaluate MIMO systems combined with HARQ. This can potentially provide higher throughput packet data services with higher reliability. Hybrid ARQ performs better than the ordinary ARQ in poor signal conditions, but this comes at the expense of significantly lower throughput in good signal conditions. HARQ can be used in MIMO systems to combat inter stream interference in addition to noise and channel gain fluctuations caused by fading. 2. RELATED WORK Lin.S et al., (1984) proposed different error control schemes for ARQ. RCPC code is used with retransmission packet size and code rate varies according to channel condition. For this Adaptive scheme, the cell loss rate and throughput efficiency are analyzed and found to be better than existing ones [1].

Ding. Z et al.,(2007) proposed a Hybrid ARQ model combined with MIMO systems to improve performance and control bit error rate. To overcome the challenges in wireless networks, this paper suggests to design combining schemes with the objective of directly optimizing the log-likelihood ratio (LLR) values. Using this approach, this paper proposes several combining schemes and then analyzes them based on three key design factors decoding performance, scalability, and memory requirement. Computer simulations under the IEEE 802.16e standard settings show the performances of the proposed combining schemes, which align well with the analysis. Based on the analyses and the simulation results, this paper suggests preferable combining schemes respectively for MIMO systems with HARQ-Chase combining (HARQ-CC) and HARQ-incremental redundancy (HARQ-IR) [5].

Jang et al.,(2007) proposed a scheme in which Hybrid ARQ techniques use Forward Error Correction (FEC) with the automatic repeat request (ARQ) protocol to recover erroneous packets caused by the channel noise and interferences. Furthermore through proper arrangement of the retransmitted packets, one can improve the performance of a MIMO system. However, most of the study of hybrid ARQ techniques is focused on scalar channels [6]. Amours et al.,(2007) explained the concept of parity bit selection permutation in MIMO-CDma systems. The utilization of bandwidth and bit error rate performance was found to be better than the existing schemes [8].

Proakis (2001) proposed the concept of Spatial Multiplexing using MIMO. Their Newyork McGraw-Hill fourth Edition issued on Digital communications emphasized applications using spatial multiplexing to wireless broadcast [10].

Tarokh (1999) proposed diversity technique, which uses multiple antennas at transmitter

side to improve the received SNR at receiver resulting in improvement of BER performance of the system[9].



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Song (2005) reports that digital communication in a fading environment when the channel

characteristic is known at the transmitter but is unknown at the receiver. This is the first report addressing the new architecture where the signals are layered in space and time as suggested by a tight capacity bound. The author also emphasizes that an extraordinary spectral efficiency near Shannon bound can be achieved in MIMO system. This new architecture targets application in future generations of fixed wireless systems. This architecture is called BLAST [11]. 3. PROPOSED WORK The existing MIMO-CDMA architecture consists of BPSK modulation. In order to improve the bit error rate performance and error correction, HARQ along with 64-QAM modulation scheme is proposed. The architecture of the proposed system is shown below.

Fig 3.1 MIMO-HARQ with QAM system In the proposed architecture, the transmitted signals are converted in to packets and then encoded using convolutional encoder. The interleaver is used for reducing noise in the transmitted bits. Then S/P converter is used for converting the serial input into parallel bits. Then the QAM modulation scheme is implemented. The inverse Fourier transform is used for signal conversion and is passed through the Rayleigh channel. In the receiver section, the reverse process of transmission is done through FFT, 64-QAM demodulation, P/S conversion, Deinterleaver and viterbi decoder. Before and after interleaving, the bit error rate calculation is done and bit error rate performance is calculated. QAM is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying (ASK). The two carrier waves, usually sinusoids, are out of phase with each other by 90°and are thus called quadrature components .The modulated waves are summed, and the resulting waveform is a combination of both phase-shift keying (PSK) and amplitude-shift keying (ASK), or (in the analog case) of phase modulation (PM) and amplitude modulation. The process of QAM modulation and demodulation is shown in fig 3.2 and 3.3.



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Fig 3.2 QAM modulator

Fig 3.3 QAM demodulator

The HARQ unit is responsible for handling the HARQ functionalities of all mobile terminals. There is one HARQ functional entity per mobile terminal in UTRAN. Each functional entity can manage up to eight parallel stop-and-wait HARQ processes.

The HARQ unit does the following functionalities:

• As the input, the HARQ entity receives the acknowledgment (ACK/NAK) from the mobile terminal.

• The HARQ entity is responsible for setting the queue ID in transmitted MAC-hs PDUs. • It also sets the transmission sequence number (TSN) in transmitted MAC-hs PDUs. The TSN

is set to value 0 for the first MAC-hs PDU transmitted for one HS-DSCH and queue ID and it is increased by one for each subsequent transmitted MAC-hs PDU. It determines a suitable HARQ process to service the MAC-hs PDU and sets the HARQ process identifier accordingly.



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4. IMPLEMENTATION

Fig 4.1: 64QAM modulation technique having 4*4 Antenna systems in Matlab

Fig 4.2: Output of the MIMO System using HARQ coding technique for 4x4 Antenna systems.



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Fig 4.3 Output of the MIMO System using HARQ coding technique for2x2 antenna systems.

Fig 4.4 The BPSK modulation scheme implemented in VLSI verilog module interfaced with

MATLAB using J-Tag



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Fig 4.5 Performance comparison between BPSK and QAM

Hence the different schemes for MIMO CDMA system implementing the 64 QAM modulation scheme have been studied and the results have been obtained and one module implemented in the VLSI domain has also been shown in the figures above. All the outputs which have been shown above are the plots of the Signal to Noise Ratio (SNR or Eb/No) versus the BER for different techniques used in the different phases of the project. The first output is the BER when 64 QAM is used and shows the compared result when different number of antenna are used and it is seen at an SNR of 28, we get a BER of 10-275. The second simulation result shows the same plot when Hybrid ARQ technique is used and it is seen that we get about a BER of 10-5.7 for an SNR of 16 when multiple antennas are used and when a single antenna is used, we get 10-4.3 at an SNR of 14.The implementation of a part of the MIMO system using VLSI is shown in fig 4.4. MATLAB is interfaced to a SPARTAN-3 VLSI kit using a JTAG and BPSK modulation was implemented in the kit.

5. CONCLUSION

The different schemes for MIMO –CDMA system implementing the 64- QAM modulation are studied and results are simulated. A part of the MIMO-CDMA architecture is also implemented using VLSI. The bit error rate performance is reduced using HARQ compared to ordinary QAM. Thus the throughput and reliability is improved in the proposed system.

6. REFERENCES [1] S. Lin, D. J. Costello, Jr., and M. J.Miller, “Automatic- Repeat Request Error-

Control Schemes,” IEEE Commun. Mag., vol. 22, Dec. 1984, pp. 5–17. [2] IEEE Std. 802.16e-2005, “IEEE Standard for Local and Metropolitan Area

Networks, Part 16: Air Interface for Fixed Broadband Wireless Access Systems, Amendment2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands,”Feb. 2006.

[3] 3GPP TS 25.201 V8.0.0 (2008-03), “3rd Generation Partnership Project; Technical



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Specification Group Radio Access Network; Physical Layer — General Description (Release 8).”

[4] K. R. Narayanan and G. Stüber, “A Novel ARQ Technique Using the Turbo Coding Principle,” IEEE Commun. Lett., vol. 1, no. 2, Mar. 1997, pp. 49–51.

[5] Z. Ding and M. Rice, “Hybrid-ARQ Code Combining for MIMO Using Multidimensional Space-Time Trellis Codes,” Proc. IEEE ISIT ’07, Glasgow, Scotland, June 2007.

[6] E. W. Jang et al., “Optimal Combining Schemes for MIMO Systems with Hybrid ARQ,” Proc. IEEE ISIT ’07, Nice, France, June 2007.

[7] C. D’Amours, “Parity bit selected spreading sequences: a block codingapproach to spread spectrum,” IEEE Commun. Lett., vol. 9, pp. 16-18, Jan. 2005.

[8] C. D’Amours and J.-Y. Chouinard, “Parity bit selected and permutation spreading for CDMA/MIMO systems,” in Proc. IEEE Veh. Tech. Conf.,pp. 1475-1479, Apr. 2007.

[9] V. Tarokh, H. Jafarkhani, and A. R. Calderbank, “Space-time block codes from orthogonal designs,” IEEE Trans. Inf. Theory, vol. 45, pp. 1456-1467, July 1999.

[10] J. G. Proakis, Digital Communications, 4th. ed. New York: McGraw-Hill,2001.

[11] Y. Song, “Parity bit selected spreading sequences for spread spectrum and code division multiple access systems,” M. A. Sc thesis, University of Ottawa, 2005.



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Performance Mimo Cdma Harq 64 Qam