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A constellation rotated quasi-orthogonal OFDM system could offer full rate and full diversity in a frequency selective fading channel. Time spreading can give additional time diversity gain in a fast fading channel. In this paper, we propose and verify a time-spread quasi-orthogonal space-frequency coded OFDM (TS-QO-SF-OFDM) system with constellation rotation. Assuming perfect channel state information...
This paper presents a joint adaptive modulation and coding (AMC) scheme, which exploits the coherence bandwidth of the wireless channel to divide the transmitted frame into independent sub-channels that correspond to the channel coherence bandwidth. This strategy is implemented for orthogonal frequency division multiplexing (OFDM) systems with channel state information (CSI) feedback. Low density...
In this work we analyse the performance of a joint coding-precoding scheme for OFDM systems over fading channels. The design of the precoder is based on the information redistribution of the input modulated symbols amongst all the output precoded symbols. The proposed precoder decreases the variance of the instantaneous noise power at the receiver produced by the channel variability. In this sense,...
Orthogonal frequency division multiplexing (OFDM) based multiple access systems have found their applications in many wireless communication systems. However, similar to conventional OFDM systems, they have a major drawback that their signal waveforms have a large peak-to-average power ratio (PAR). The resulting systems have low power amplifier efficiency, which is prohibitive for battery driven terminals...
Recently, to meet higher data rate requirements, LDPC coded MIMO-OFDM systems are investigated widely. Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (OFDM) is an attractive solution for next-generation wireless local area networks (WLANs). Space-time block coded OFDM is capable of achieving substantial diversity gains, while...
The multipath diversity and coding gain metrics for cyclic-prefixed single-carrier (SC-CP) systems, which characterize the bit error rate (BER) at high SNR, have not been carefully studied in the literature. We first show that, unlike OFDM, the diversity and coding gains for SC-CP are data-realization-dependent. Then, we show that there is a signal-to-noise ratio (SNR) threshold beyond which the dominant...
European terrestrial digital video broadcasting (DVB-T) standard has been launched based on the well knows modulation technique; orthogonal frequency division multiplexing (OFDM), which when used in conjunction with channel coding is known as COFDM. This paper will show the efficiency of COFDM in different DVB-T environments based on a compliant DVB-T simulation. An efficiency performance study of...
Selected Mapping (SLM) is a popular technique used for Peak-to Average Power (PAPR) reduction in OFDM systems. Normally SLM techniques require explicit side information to be transmitted to allow decoding at the receiver. Alternative SLM techniques use shift register scramblers to embed the side information into the transmitted OFDM symbols. In this paper the concept of an SLM Simplified Scrambler...
In this paper, we study the effect of various concatenated forward error correction (FEC) codes on the performance of a wireless orthogonal frequency division multiplexing (OFDM) system. In FEC concatenated channel code, the OFDM system incorporates Reed-Solomon (RS) encoder of (255,239,8), Cyclic Encoder of (15,11), Bose-Chadhuri-Hocquenghem (BCH) encoder of (127,64) with Convolution encoder of 2...
The modern telecommunication industry demands higher capacity networks with high data rate. Orthogonal frequency division multiplexing (OFDM) is a promising technique for high data rate wireless communications at reasonable complexity in wireless channels. OFDM has been adopted for many types of wireless systems like wireless local area networks such as IEEE 802.11a, and digital audio/video broadcasting...
The bit error rate (BER) performance analysis of an OFDM wireless communication system is carried out considering the effect of fading and multipath dispersion. Analysis is extended to include multiple-input and multiple output (MIMO) transceiver configuration to combat the effect of fading. Further, forward error correction coding such as convolutional coding (CC) is also applied to improve the BER...
In spectrum pooling applications, the spectral leakage of DFT-based OFDM systems should be divided into two parts, in-band-out-of-subband (IBOSB) leakage and out-of- band (OOB) radiation. A scheme is proposed to suppress the IBOSB leakage and redistribute OOB radiation through the frequency domain correlative coding with appropriate weighting. It introduces the correlation between adjacent subcarriers,...
Intercarrier interference (ICI) self-cancellation schemes were often employed in many OFDM systems as a simple and effective approach to suppress ICI caused by carrier frequency error. In this paper, we propose a space time frequency block coding technique MIMO-OFDM system with ICI self-cancellation of data conjugate method, which is capable of both error correction and ICI reduction produced by the...
Orthogonal frequency division multiplexing (OFDM) communication systems, the frequency offsets in mobile radio channels distort the orthogonality between subcarriers resulting in intercarrier interference (ICI). This paper studies an efficient ICI cancellation method termed ICI self-cancellation scheme. The scheme works in two very simple steps. At the transmitter side, one data symbol is modulated...
Based on the principle of spread spectrum systems, this paper presents a hybrid automatic-repeat-request (HARQ) scheme with the mitigation of intercarrier interference (ICI) by orthogonally encoding transmitted signals on subcarriers for orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme not only increases the signal-to-noise ratio (SNR) but also reduces the ICI. Simulations...
When spectral nulls are present in a channel, they can severely degrade or cancel out OFDM tones, resulting in an irreducible error rate. In Code Spread OFDM, each sinewave carries a weighted sum of all the information symbols being transmitted in an OFDM block interval. This creates a more robust modulation scheme which provides substantial performance improvement relative to standard OFDM. In this...
This paper highlights the space time frequency block codes (STFBC) that exploit spatial, time and frequency diversity can be designed using orthogonal frequency division multiplexing (OFDM). However, OFDM suffers from ICI. Hence, a new OFDM-MIMO using STFBC method combining ICI-SC scheme is investigated to reduce ICI and error correction effectively. The technique of reducing ICI using Space Time...
In this paper, we present a floating-point model for OFDM part of the IEEE 802.16a standard. This part has been assigned as the mandatory structure for WiMax. Next, we present a bit-true model for Viterbi decoder and encoder of it with the constraint of having less than 0.5 dB degradation in the performance of the system while minimizing the hardware cost of it. Since the most sensitive modulation...
In OFDM systems, the inter-symbol interference and inter-block interference are eliminated by using null-tones (NT) and cyclic prefix (CP) redundancy of length higher than the channel size. To preserve a high bit rate, channel shortening method is required to reduce the redundancy. Recently, channel shortening technique with differential encoded OFDM systems without the NT was introduced. This technique...
In wireless communication systems, intended to support broadcast services, it is not feasible to use an error control strategy such as automatic repeat request (ARQ) due to the heavy channel and transmitter load caused by all repeat-requests. An alternative error correcting strategy not suffering from the disadvantages of using ARQ is the introduction of a forward error correcting (FEC) code. In this...
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