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The use of hybrid automatic-repeat-request (HARQ) with multi-antenna systems (MIMO) promises high throughput with high reliability in broadband wireless communication systems. One of the combining methods in MIMO-HARQ is by directly optimizing the log-likelihood ratio (LLR) values instead of compensating the multiple signal-to-interference-and noise power ratios (SINRs) as in conventional combining...
In the frame of block pilot channel estimation, an ameliorated version of the Least Squares (LS) algorithm is here proposed for OFDM systems. Former studies use the fact that the cyclic prefix (CP) duration upper bounds the length of the channel impulse response (CIR) to cancel the estimation noise lying outside the CIR first taps, equal in number to the CP samples. However, if the channel is sparse,...
When the cyclic prefix is less than channel memory or under clipping noise in Orthogonal Frequency Division Multiplexing (OFDM) detection, a good Bit Error Rate (BER) performance is achieved using the Maximum Likelihood Block Detector (MLBD). However, the computational load at the receiver is high under this condition. It is well known that conventional GA based approach offers less computation for...
A two-stage data detection algorithm is presented to simplify the receiver structure for long intersymbol interference (ISI) channel. After partial ISI elimination by a minimum mean square error (MMSE) equalizer, the following fast windowed Chase equalization (FWCE) can ensure bit error rate (BER) performance approaching the maximum likelihood sequence detection (MLSD). Compared with the WCE algorithm,...
Multiple-input double-output (MIDO) codes are important in future wireless communications, where the portable end-user device is physically small and will typically contain maximum two receive antennas. Especially tempting is the 4×2 channel, where the four transmitters can either be all at one station, or separated between two different stations. Such channels optimally employ rate-two space-time...
This study addresses the general problem of efficient resource management in wireless networks with arbitrary time-varying topologies. Communication channels are assumed to generally accommodate multiple simultaneous transmissions. In this context, we focus our attention on the problem of distributed transmission power allocation and medium access by links (transmitter-receiver pairs) that require...
MIMO communication is a core technology for wireless systems. This work presents an improved fixed complexity detection technique for underdetermined and overdetermined MIMO systems, based on a low complexity, diversity optimal, incremental channel partition. This new algorithm also employs a new efficient tree search implementation of the precancellation step. Because of these improvements, this...
A common technique for cognitive radio wideband spectrum sensing is energy/power detection of primary users (PU) in frequency domain. Specifically, power spectrum estimation methods are combined with power detection statistics to test the PU presence. However, when detecting in a particular band of interest these techniques suffer from energy leakage and adjacent channel interference. In this paper,...
We propose a quantization scheme based on a Kd (K dimensional)-tree algorithm for signature sequence in a reverse-link direct sequence (DS)-code division multiple access (CDMA). With a few feedback bits, a receiver quantizes the optimal signature that minimizes interference for a desired user, and relays it to the user via an error-free feedback channel. A user performance depends on the quantization...
In this paper, we consider cooperative networks comprising multiple simultaneous transmitting source-destination pairs. Specifically, we propose two relay assignment schemes whereby one relay is assigned to one pair at any given time. It is assumed that the number of relays equals or exceeds the number of pairs. This assumption is practical because in future wireless networks, any node in the network...
Adaptive OFDM technology is the real-time response of the transmitter according to the time-varying channel, it has been widely applied to wireless channels with multi-path interference to build high-speed, reliable communication links. At present, Campello algorithm should be the relatively outstanding adaptive OFDM algorithm in comparison, but it needs a great amount of computation. Hence, we proposes...
In this paper, we investigate channel allocation for cooperative relays in cognitive radio networks. Different from conventional cooperative relay channels, cognitive radio relay channels are actually a combination of three kinds of channels: direct, dual-hop, and relay channels, which belong to different spectrum bands and provide parallel end-to-end transmission. In order to maximize the achievable...
Space time codes (STC) have been shown to be used well with the Multiple Input Multiple Output (MIMO) channel. The Orthogonal STC (OSTC) family of codes is known to achieve full diversity as well as very simple implementation of the Maximum Likelihood (ML) decoder. However, it was proven that with a complex symbol constellation one cannot achieve a full rate code when the number of transmitting antennas...
Resources allocation of OFDM system is a key factor that affects system performance. Parteek Bansal proposed a bit-power allocation algorithm under different bit error rate (BER). But the process of its bit allocation will cause high complexity and bad real-time to build a power-increment table. In this paper, a low-complexity multi-user subcarrier-bit-power allocation algorithm for wireless OFDMA...
Multiple-input multiple-output (MIMO) technologies have the advantage of improving system throughput and error performance by exploiting the spatial diversity, owing to the multiple independent transmit-receive paths. A lot of efforts have been put into MIMO broadcast channels research and it is expected to be a core technology for 3G and 4G wireless systems. Generally, channel state information (CSI)...
In this work an efficient low-complexity user selection algorithm for the multiuser MISO downlink wireless channel is presented. The algorithm combines Zero-Forcing linear precoding with low-complexity correlation-based Space Division Multiple Access (SDMA) and aims at maximizing the sum rate of all system users. The complexity of the algorithm is analyzed and is shown to be lower than previously...
In this paper, a novel effective low-complexity single carrier frequency-domain equalization SC-FDE scheme in multiple-input multiple-output (MIMO) system is introduced under frequency selective channel. It contains the advantages of SC-FDE and the complexity decreasing in MMSE algorithm by frequency-domain QR (FD-QR) decomposition. Also a rearrangement is implemented according to signal to noise...
As a well attractive modulation scheme, minimum-shift keying (MSK) has a fast roll-off side-lobe spectrum. Because of this excellent property, we introduce MSK into the conventional OFDM to form an improved OFDM-MSK system. The new system can effectively overcome the carrier frequency offset (CFO), mitigate the interference among the sub-carriers. And two kinds of OFDM-MSK receiver are discussed in...
We consider the problem of detecting a primary signal over a wireless channel by a multiantenna cognitive spectral monitor with knowledge of the spectral shape of primary transmissions employing multicarrier modulation. As a starting point, a Locally Most Powerful (LMP) test is derived for the single-antenna case. The asymptotic performance improvement of the LMP detector over the standard Energy...
Single carrier transmission with cyclic prefix (SC- CP) has been adopted in wireless applications as an alternative air interface to orthogonal frequency division multiplexing (OFDM). In this paper, we compare the time and frequency domain equalization schemes utilizing regular LDPC codes in SC-CP system. Simulation results show that CP can be employed for better decoding in a multipath environment...
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