Reception for Layered STBC Architecture in WLAN Scenario Piotr Remlein Chair of Wireless Communications Poznan University of Technology Poznan, Poland e-mail: remlein@et.put.poznan.pl Hubert Felcyn Chair of Wireless Communications Poznan University of Technology Poznan, Poland e-mail: hubert.felcyn@gmail.com Abstract—In this paper, reception for multi-stream Orthogonal Frequency Division Multiplexing (OFDM) transmission is analyzed. The system architecture employs Linear Dispersion Space-Time Block Codes (LD-STBC). In the transmitter, a part of spatial streams is Space Time Block Coded (STBC). The LD-STBC-VBLAST OFDM receiver is described and analyzed. The quality of reception for Wireless- LAN (WLAN) transmission with channel type E is investigated using a computer simulation. We present the simulation results for two models of OFDM receivers. Performance of VBLAST and LD-STBC-VBLAST receivers has been compared. The Bit Error Rate (BER) and Packet Error Rate (PER) have been determined for different numbers of spatial streams in use. The results illustrate that the LD-STBC-VBLAST OFDM receiver improves the transmission quality in WLAN scenario. Keywords-multi-antenna transmission; receiver; space time block coding; wireless networks. I. INTRODUCTION In recent years, WLANs have gained on popularity. This is due to the fact that thanks to the advanced technologies they already offer high quality (with low error rate) and high speed transmissions. Simultaneously, constant grow of demand in even higher network throughput and quality transmission are observed. Therefore, insightful research on WLANs is necessary to change the existing standards [1]. As theoretical and practical research carried out lately [2-4] has shown, transmission through multi-path wireless channels may improve the system’s capacity if used adequately. According to Bäolcskei and Paulraj [3] a Multiple Input Multiple Output (MIMO) system enables increasing of a wireless channel’s capacity proportionally to the growing number of transmit and receive antennae. A practical implementation of a MIMO system is shown by Wolniansky et al. [5]. It is the so-called Vertical Bell Laboratories Layered Space Time (VBLAST) system, which has a simple structure, yet it offers high spectral efficiency. In VBLAST, a single data stream is divided into several sub-streams transmitted simultaneously by several antennae as a result of which transmission speed may be improved. Literature suggests many options to form receivers that would receive signals transmitted in MIMO system [2-5]. One of the methods is Maximum Likelihood (ML). This detection method offers the lowest error rate but is rather difficult to implement. Wolniansky et al. [5] propose MIMO signal detection based on the Zero-Forcing (ZF) criterion. The ZF method is characterized by relatively low computational requirements. However, its weakness is certainly the so-called noise enhancement occurring in the case of minor SNR values. Considerably effective detection algorithms that use the so-called QR decomposition of channel matrix have been proposed in [6] [7]. Another advantage of MIMO transmission is quality improvement with reference to drop in error rate. This is obtained by using Space Time Block Codes (STBC) [8]. The superior purpose of spatial multiplexing is to maximize data transmission speed while the essence of space-time coding is to ensure high quality resulting from maximizing the diversification. These two advantages offered by MIMOs exclude each other. The so-called Linear Dispersion (LD) method was proposed by Hassibi and Hochwald [9]. The method attempts to use both the aforesaid advantages of MIMO transmission: spatial multiplexing and diversification gain. As test results show [9-11], owing to the method high transmission speed may be obtained with any configuration of antenna systems on both sides of the radio connection with simultaneous code gain. Solutions known for the MIMO transmission, such as the VBLAST [5] algorithm or ZF, may be applied for receiving [4-7]. The LD-STBC-VBLAST method was used by the authors for OFDM transmission in a WLAN system. Simulation results for selected receive algorithms that may be used for WLAN 802.11n MIMO/OFDM system are presented. Performance, in the terms of BER, LD-STBC- VBLAST and VBLAST receivers has been compared. The analyzed system uses a multi-stream transmission in which a part of spatial streams is STBC-coded and a part is transmitted without coding. It was assumed that individual subcarriers are modulated with 2-PSK, 4-PSK or 16-QAM signal. The purpose hereof is to compare the operation of the aforesaid system for two different receivers: LD-STBC- VBLAST, using the LD (Linear Dispersion) algorithm [9] and VBLAST [5] and to check the suitability of the abovementioned receivers for the improvement of data transmission quality in WLAN 802.11n. The BER and PER were determined for the E type transmission channel model [12]. The simulation referred to transmission through E type WLAN channel because, as test 70 Copyright (c) IARIA, 2014. ISBN: 978-1-61208-347-6 ICWMC 2014 : The Tenth International Conference on Wireless and Mobile Communications