Performance Analysis of Adaptive Filter Channel Estimated MIMO OFDM Communication System

Advanced Communication Systems are wideband systems to support multiple applications such as audio, video and data so and so forth. These systems require high spectral efficiency and data rates. In addition, they should provide multipath fading and inter-symbol interference (ISI) free transmission. Multiple input multiple output orthogonal frequency division multiplexing (MIMO OFDM) meets these requirements Hence, MIMO-OFDM is the most preferable technique for long term evaluation advanced (LTE-A). The primary objective of this paper is to control bit error rate (BER) by proper channel coding, pilot carriers, adaptive filter channel estimation schemes and space time coding (STC). A combination of any of these schemes results in better BER performance over individual schemes. System performance is analyzed for various digital modulation schemes. In this paper,adaptive filter channel estimated MIMO OFDM system is proposed by integrating channel coding, adaptivefilter channel estimation, digital modulation and space time coding. From the simulation results, channel estimated 2×2 MIMO OFDM system shows superior performance over individual schemes

Adaptive redundant residue number system coded multicarrier modulation

The novel class of nonbinary maximum minimum distance redundant residue number system (RRNS) codes is invoked in the context of adaptively RRNS coded, symbol-by-symbol adaptive multicarrier modulation, in order to combat the effects of frequency-selective fading inflicted by dispersive wide-band channels. The system’s performance can be adjusted in order to maintain a given target bit error rate (BER) and bit per symbol (BPS) performance. The proposed adaptive RRNS scheme outperforms the convolutional constituent code based turbo coded benchmarker system for channel signal-to-noise ratios (SNR) in excess of about 15 dB at a target BER of 10-4. Index Terms—Adaptive channel coding, adaptive modulation, adaptive OFDM, coded multicarrier modulation, OFDM, redundant residue number system

Adaptive Channel Coding and Modulation Scheme Selection for Achieving High Throughput in Wireless Networks

Modern wireless communication demands reliable data communication at high throughput in severe channel conditions like narrowband interference, frequency selective fading due to multipath and attenuation of high frequencies. Traditional single carrier systems address this set of problems by the use of complex, computationally intensive equalization filters. The Orthogonal Frequency Division Multiplexing (OFDM) based system, as opposed to single-carrier systems, is considered to be the future of the wireless communication and is being used to achieve high data rate by overcoming severe channel conditions without the use of these complex filters.This paper discusses the problem of Adaptive Modulation scheme selection through an OFDM based system over parallel frequency selective fading channels. An adaptive coding scheme is proposed by using Generalized Concatenated Codes (GCC), which have simple structure and are designed in such a way that they are best suited for fading channels. GCC are based on binary cyclic codes. The criterion of the proposed research is to optimize the throughput of a wireless system. Depending on the quality of sub-channels an adaptive modulation selection scheme and code assigning method is proposed. The proposed research combats against channel impairments better than those used in conventional systems by exploiting individual sub-channel condition. Results show better performance in terms of higher throughput by minimizing the bit error rate

Multicarrier systems with antenna diversity for wireless commmunications

Future wireless communications systems need a high quality of service coupled with high data rate transmission for multimedia services. Achieving this goal in the hostile wireless environment with its limited spectrum has several challenges and implies the necessity of a communication system that is able to increase the channel capacity and overcome the difficulties of the wireless transmission environment with reasonable system complexity. Two of the most enabling technologies for the next generation of wireless systems are orthogonal frequency division multiplexing (OFDM) and multiple-input multiple output (MIMO) systems. MIMO systems have been originally designed for known flat fading channels. In this research, some novel MIMO-OFDM schemes for broadband wireless applications are developed and presented. The objective of the proposed schemes is to enhance the performance of OFDM systems over multipath fading channels by using antenna diversity techniques, and also to make MIMO systems applicable to frequency selective multipath fading channels. For the performance evaluation, both bit error rate (BER) and channel capacity analysis are considered. The channel capacity of MIMO-OFDM systems is analytically evaluated and it is shown that the channel capacity of the these systems can be dramatically increased as a function of the number of antennas. The BER performance of the MIMO-OFDM systems is analytically evaluated. New closed-form expressions for the BER performance of the MIMO-OFDM systems over frequency selective fading channels are derived. On the other hand, the growing popularity of both MIMO and OFDM systems creates the need for adaptive modulation to integrate temporal, spatial and spectral components together. The performance improvement offered by adaptive modulation over non-adaptive systems is remarkable. Furthermore, other dimensions such as frequency and space may yield further gains by providing additional degrees of freedom that can be exploited by adaptive modulation. In this research, a new adaptive modulation scheme for our MIMO-OFDM system (SFBC-OFDM) is presented. The proposed scheme exploits the benefits of space-frequency block codes (SFBC), OFDM and adaptive modulation to provide a high quality of transmission for wireless communications over frequency selective fading channels. It is shown that adaptive modulation can greatly improve the performance of the conventional SFBC-OFDM systems. Finally, a novel antenna selection algorithm is proposed for our MIMO-OFDM system. Three different forms of antenna selection are considered: transmit antenna selection, receive antenna selection, and joint transmit/receive antenna selection. The coding and diversity advantages of the MIMO-OFDM system with antenna selection are examined using average SNR gain, outage probability and BER analysis. The system performance of different forms of the proposed scheme is evaluated and compared. It is shown that the proposed scheme can greatly improve the performance of the conventional SFBC-OFDM systems

Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems

Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER

Adaptive spatial mode of space-time and spacefrequency OFDM system over fading channels

In this paper we present a 2 transmit 1 receive (1 Tx : 1 Rx) adaptive spatial mode (ASM) of space-time (ST) and space-frequency (SF) orthogonal frequency division multiplexing (OFDM). At low signal to noise ratio (SNR) we employ ST-OFDM and switch to SF-OFDM at a certain SNR threshold. We determine this threshold from the intersection of individual performance curves. Results show a gain of 9 dB (at a bit error rate of 10-3) is achieved by employing adaptive spatial mode compared to a fixed ST-OFDM, almost 6 dB to fixed SF-OFDM, 4 dB to Coded ST-OFDM and 2 dB to a fixed coded SF-OFDM, at a delay spread of 700 ns

Space-Time Trellis and Space-Time Block Coding Versus Adaptive Modulation and Coding Aided OFDM for Wideband Channels

Abstract—The achievable performance of channel coded spacetime trellis (STT) codes and space-time block (STB) codes transmitted over wideband channels is studied in the context of schemes having an effective throughput of 2 bits/symbol (BPS) and 3 BPS. At high implementational complexities, the best performance was typically provided by Alamouti’s unity-rate G2 code in both the 2-BPS and 3-BPS scenarios. However, if a low complexity implementation is sought, the 3-BPS 8PSK space-time trellis code outperfoms the G2 code. The G2 space-time block code is also combined with symbol-by-symbol adaptive orthogonal frequency division multiplex (AOFDM) modems and turbo convolutional channel codecs for enhancing the system’s performance. It was concluded that upon exploiting the diversity effect of the G2 space-time block code, the channel-induced fading effects are mitigated, and therefore, the benefits of adaptive modulation erode. In other words, once the time- and frequency-domain fades of the wideband channel have been counteracted by the diversity-aided G2 code, the benefits of adaptive modulation erode, and hence, it is sufficient to employ fixed-mode modems. Therefore, the low-complexity approach of mitigating the effects of fading can be viewed as employing a single-transmitter, single-receiver-based AOFDM modem. By contrast, it is sufficient to employ fixed-mode OFDM modems when the added complexity of a two-transmitter G2 scheme is affordable