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The performance of OFDM transmission over frequency selective fading radio channels can be improved by spreading the data elements of each OFDM symbol over all OFDM subcarriers. This known approach to frequency diversity is termed Full Data Spreading (FDS) and would render data detection prohibitively complex. In order to affordably seize the advantage of frequency diversity by data spreading, we...
In this paper we study the statistical distribution of the enhanced noise after zero forcing frequency domain equalization in an OFDM system transmitting over a Nakagami-m fading channel. With this purpose, we obtain the expression of the density function of the ratio between the modulus of a complex Gaussian random variable (i.e., a Rayleigh distributed random variable) and that of a n-dimensional...
In this paper, we propose a novel transmit signal structure for OFDM (orthogonal frequency division multiplexing). Instead of the conventional cyclic prefix (CP), we use a deterministic sequence, which we call unique word (UW), as guard interval. We show how unique words, which are already well investigated for single carrier systems with frequency domain equalization (SC/FDE), can also be introduced...
This paper deals with the interference mitigation problem of the distributed space time block coded (STBC) amplify-and-forward (AF) cooperative orthogonal frequency division multiplexing (OFDM) signal in the presence of carrier frequency offsets (CFO). Multiple CFOs introduce phase drift, inter-carrier interference (ICI) and inter-block interference (IBI) to the received signal. A joint time domain...
Recent years, Orthogonal Frequency Division Multiplexing (OFDM) has been widely applied to various digital communication systems. WiMAX (Worldwide Interoperability for Microwave Access) holds a combination of fixed and mobile broadband wireless access techniques. IEEE 802.16e is the specification designed for WiMAX system in application of mobile environments. In order to achieve robust performance,...
Recently there is a noticeable interest in investigation of the squared norm distribution of complex-valued Gaussian variables that have different variances. A typical example is consideration of the channel state information (CSI) in multi-antenna systems. A similar problem appears in communication systems interfered by Middleton Class A impulsive noise. In this paper we develop exact expressions...
In this paper, we propose the new channel estimation algorithm in frequency domain for orthogonal frequency division multiplexing (OFDM) system in fast fading channels. In this algorithm first we estimate channel response at pilot subcarriers then interpolate channel response at data subcarriers by Gaussian Radial basis function as an efficient nonlinear interpolator. At next step by filtering and...
Orthogonal frequency division multiplexing (OFDM) is noted for its resistance to narrowband interference when equipped with forward error correction. This technique along with erasure insertion is adequate when the the signal-to-interference ratio (SIR) is moderate, around 0 dB, however, when the interference is severe, i.e. SIR = -20 dB, a non-orthogonal interference corrupts a large number of the...
To deal with the multi-path delay spread in non- line-of-sight (NLOS) environments, single-carrier frequency- domain equalization (SC-FDE), a.k.a., single-carrier block transmission (SCBT), is thought to be an effective alternative of orthogonal frequency division multiplexing (OFDM). On the other hand, the low-density parity-check (LDPC) coding is considered as the high-performance channel coding...
In orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems, the sub-carriers, which span the spectrum used by licensed users (LUs), should be deactivated to avoid interference. The resulted OFDM system is called non-contiguous OFDM (NC-OFDM) system. For NC-OFDM systems, as no pilot symbols can be transmitted over these deactivated subcarriers, the conventional modified...
Narrowband communications over power lines has been in use for automatic meter reading (AMR) of electric, gas, and water meters. The major hurdle in the widespread use of this medium is the time varying nature of the channel and impairments such as the presence of colored background noise and large impulse noises in time and frequency domains. In this paper, we model the extremely noisy channel environment...
One of the main disadvantages of Orthogonal Frequency Division Multiplexing (OFDM) is its high peak-to- average power ratio (PAPR). As the simplest approach to reducing the PAPR, clipping exhibits good practicability, and the repeated clipping-and-filtering (RCF) algorithm proposed by Jean Armstrong provides a good performance in PAPR reduction and out-of-band power's filtering. However, its way of...
Orthogonal frequency division multiplexing (OFDM) is the modulation scheme of choice for digital video broadcasting-handheld (DVB-H), which is required to operate under high mobility conditions resulting in significant Inter-carrier Interference (ICI). To mitigate ICI, several cancellation schemes have been proposed but they require reliable channel information at the receiver which is quite challenging...
Some communication applications, like multimedia, deliver data of different importance classes allowing unequal error protection (UEP) levels. In this paper, a multiple-input multiple-output (MIMO) system using orthogonal frequency division multiplexing (OFDM) is considered with a new UEP bit-loading algorithm based on the non-UEP algorithm by Chow, Cioffi, and Bingham. In the proposed bit-loading...
Orthogonal frequency division multiplexing (OFDM) is the modulation scheme of choice for digital video broadcasting-handheld (DVB-H) which is required to operate under high mobility conditions resulting in significant Inter-Carrier Interference (ICI). Under these conditions, the conventional one-tap per subcarrier channel estimation and equalization is suboptimal since it does not account for ICI...
Effects of improved channel estimation are studied for a proposed IEEE 802.11n OFDM MIMO system. Three channel estimation methods are considered: maximum likelihood (ML), time-domain truncation (TDT) and model-based (MB). TDT and MB are particularly useful when the channel delay spread is short. For an MMSE receiver, MB shows a 1-2.5 dB improvement over ML on the packet error rate performance for...
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