共查询到20条相似文献,搜索用时 15 毫秒
1.
A low complexity soft-input soft-output (SISO) block decision feedback equalizer (BDFE) is presented for turbo equalization. The proposed method employs a sub-optimum sequence-based detection, where the soft-output of the equalizer is calculated by evaluating an approximation of the sequence-based a posteriori probability (APP) of the data symbol. The sequence-based APP approximation is enabled by the adoption of both soft a priori information and soft decision feedback, and it leads to better performance and faster convergence compared to symbol-based detection methods as used by most other low complexity equalizers. The performance and convergence property of the proposed algorithm is analyzed by using extrinsic information transfer (EXIT) chart. Both analytical and simulation results show that the new equalizer can achieve a performance similar to that of trellis-based equalization algorithms, with a complexity similar to linear SISO minimum mean square error equalizers. 相似文献
2.
The Signal‐to‐Interference Ratio (SIR) has been highlighted in the literature to be a most efficient criterion for several methods aiming at reducing the effects of cochannel interference, e.g., diversity reception, dynamic channel allocation and power control. In this paper we address the problem of how to obtain fast and accurate measurements of this parameter in a practical context. We develop a general SIR estimation technique for narrow‐band cellular systems that is based on a signal subspace approach using the sample covariance matrix of the received signal. Simulation results using the frame structure in the GSM system show that the SIR can be estimated to within an error of 0.3 dB after only 200 ms, or within an error of 0.1 dB after only 0.6 seconds. 相似文献
3.
The Signal‐to‐Interference Ratio (SIR) has been highlighted in the literature to be a most efficient criterion for several
methods aiming at reducing the effects of cochannel interference, e.g., diversity reception, dynamic channel allocation and
power control. In this paper we address the problem of how to obtain fast and accurate measurements of this parameter in a
practical context. We develop a general SIR estimation technique for narrow‐band cellular systems that is based on a signal
subspace approach using the sample covariance matrix of the received signal. Simulation results using the frame structure
in the GSM system show that the SIR can be estimated to within an error of 0.3 dB after only 200 ms, or within an error of
0.1 dB after only 0.6 seconds.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
A Simple and useful decision feedback equalizer used for non-linear channels with severe linear distortion and mild non-linear distortion is proposed. It is a combination of a nonlinear channel equalizer based on connectionist model and a common decision feedback equalizer for linear channels. For a typical non-linear channel model it is shown that the equalization performances of the proposed equalizer are improved significantly. 相似文献
5.
Distributed multiuser detection for the TDMA cellular uplink 总被引:1,自引:0,他引:1
A method for performing multiuser detection using observations from multiple base stations is proposed. Log-likelihood ratio estimates of the data are calculated at each base station and combined to form the final decision statistic. The proposed architecture is applied to the time division multiple access (TDMA) cellular uplink, and it is shown that heavily overloaded systems can perform remarkably well 相似文献
6.
In-service signal quality estimation for TDMA cellular systems 总被引:1,自引:0,他引:1
In-service interference plus noise power (I+N) and signal-to-interference plus noise power S/(I+N) estimation methods are examined for TDMA cellular systems. A simple (I+N) estimator is developed whose accuracy depends on the channel and symbol estimate error statistics. Improved (I+N) and S/(I+N) estimators are developed whose accuracy depends only on the symbol error statistics. The proposed estimators are evaluated through software simulation with an IS-54 frame structure. For high speed mobiles, it is demonstrated that S/(I+N) can be estimated to within 2 dB in less than a second.This research was funded by Bell Northern Research, Inc., and completed while Dr. Austin was a Ph.D. student at the Georgia Institute of Technology. 相似文献
7.
Xiao-An Wang Wicker S.B. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1996,42(2):543-553
In order to fully utilize the SDD (soft-decision decoding) capacity of the outer codes in a concatenated system, reliability information on the inner decoder outputs (called soft outputs) needs to be provided to the outer decoder. This paper shows that a modified MAP algorithm can be effectively and accurately used to generate such information. In the course of the presentation, a metric based on the reliability information is proposed for the outer decoder. This metric has the Euclidean metric on AWGN channels as its special case, which leads to the concept of generalized SDD (GSDD). Several practical concerns regarding the proposed soft-output decoder are addressed through theoretical analysis and simulation: the effect of finite decoding depth, computational complexity, range overflow, and scaling. Comparisons to previous work on soft-output decoders are made 相似文献
8.
Hoeher P.A. Badri-Hoeher S. Shiyang Deng Krakowski C. Wen Xu 《Wireless Communications, IEEE Transactions on》2006,5(6):1234-1237
In this letter, single antenna co-channel interference cancellation for cellular time-division multiple access (TDMA) networks by means of joint delayed-decision feedback sequence estimation is studied. The performance is increased by a novel adaptive state allocation technique. 相似文献
9.
Capacity of digital cellular TDMA systems 总被引:1,自引:0,他引:1
The capacity of digital TDMA (time-division multiple-access) systems is addressed. It is projected that capacity improvement will be of the order of 5-10 times that of analog FM without adding any cell sites. For example, the North American TIA (Telecommunication Industry Association) standard offers around 50 Erlang/km2 with a 3-km site-to-site distance. In addition, the TDMA principle allows a faster handoff mechanism (mobile assisted handoff), which makes it easier to introduce microcells with a cell radius of about 200 m. This gives substantial additional capacity gain beyond the 5-10 factor given above. TDMA makes it possible to introduce adaptive channel allocation (ACA) methods. ACA is a mechanism that provides efficient microcellular capacity. ACA also eliminates the need to plan frequencies for cells. It is concluded that the air-interface of digital TDMA cellular may be used to build personal communication networks 相似文献
10.
In TDMA system each channel may have more than one time slot to serve more than one user. Techniques for the assignment of time slots to users while minimizing co-channel interference are important. The paper presents six time slot assignment techniques. A discrete event stochastic simulation study was performed on 120° and 60° sectored systems. The simulation employs the “blocked calls cleared” traffic model and a log-linear path loss propagation model. Only the down link is considered. The results compare the performance of the six techniques and investigates the effect of the number of time slots per frame and the maximum acceptable interference level 相似文献
11.
Co-channel interference cancellation is particularly challenging in the downlink of cellular radio systems because usually only one receive antenna is available at the mobile terminal. This tutorial provides an overview of promising a single-antenna co-channel interference cancellation techniques. Focus is on the downlink of time-division multiple access systems. The results may, however, be extended to related applications, including interference suppression in multiple-input multiple-output systems. 相似文献
12.
A novel fast algorithm for computing the minimum MSE decision feedback equalizer settings is proposed. The equalizer filters are computed indirectly, first by estimating the channel, and then by computing the coefficients in the frequency domain with the discrete Fourier transform (DFT). Approximating the correlation matrices by circulant matrices facilitates the whole computation with very small performance loss. The fractionally spaced equalizer settings are derived. The performance of the fast algorithm is evaluated through simulation. The effects of the channel estimation error and finite precision arithmetic are briefly analyzed. Results of simulation show the superiority of the proposed scheme 相似文献
13.
Gen-Kwo Lee Gelfand S.B. Fitz M.P. 《Selected Areas in Communications, IEEE Journal on》1995,13(1):155-166
There has been great interest in reduced complexity suboptimal MAP symbol-by-symbol estimation for digital communications. We propose a new suboptimal estimator suitable for both known and unknown channels. In the known channel case, the MAP estimator is simplified using a form of conditional decision feedback, resulting in a family of Bayesian conditional decision feedback estimators (BCDFEs); in the unknown channel case, recursive channel estimation is combined with the BCDFE. The BCDFEs are indexed by two parameters: a “chip” length and an estimation lag. These algorithms can be used with estimation lags greater than the equivalent channel length and have a complexity exponential in the chip length but only linear in the estimation lags. The BCDFEs are derived from simple assumptions in a model-based setting that takes into account discrete signalling and channel noise. Extensive simulations characterize the performance of the BCDFE and BCDPE for uncoded linear modulations over both known and unknown (nonminimum phase) channels with severe ISI. The results clearly demonstrate the significant advantages of the proposed BCDFE over the BCDFE in achieving a desirable performance/complexity tradeoff. Also, a simple adaptive complexity reduction scheme can be combined with the BCDFE resulting in further substantial reductions in complexity, especially for large constellations. Using this scheme, we demonstrate the feasibility of blind 16QAM demodulation with 10-4 bit error probability at E b/N0≈ 18.5 dB on a channel with a deep spectral null 相似文献
14.
A decision feedback equalizer with time-reversal structure 总被引:1,自引:0,他引:1
This work describes the use of a receiver with a time-reversal structure for low-complexity decision feedback equalization of slowly fading dispersive indoor radio channels. Time-reversal is done by storing each block of received signal samples in a buffer and reversing the sequential order of the signal samples in time prior to equalization. As a result, the equivalent channel impulse response as seen by the equalizer is a time-reverse of the actual channel impulse response. Selective time-reversal operation, therefore, allows a decision feedback equalizer (DFE) with a small number of forward filter taps to perform equally well for both minimum-phase and maximum-phase channel characteristics. The author evaluates the theoretical performance bounds for such a receiver and quantifies the possible performance improvement for discrete multipath channels with Rayleigh fading statistics. Two extreme cases of DFE examples are considered: an infinite-length DFE; and a DFE with a single forward filter tap. Optimum burst and symbol timing recovery is addressed and several practical schemes are suggested. Simulation results are presented. The combined use of equalization and diversity reception is considered 相似文献
15.
A new algorithm is proposed for estimating the signal-to-interference plus noise ratio S/(I+N) in time-division multiple-access (TDMA) cellular systems. The S/(I+N) estimator is evaluated for use in the IS-54/136 system and a GSM-like system, and compared with existing techniques. The algorithm has a mean square prediction error that is comparable to the best known S/(I+N) estimation schemes, but with a significantly reduced computational complexity 相似文献
16.
Ghosh M. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1998,86(10):2070-2081
In December 1996 the Federal Communications Commission (FCC) adopted the Grand Alliance (GA) system as the digital television broadcasting standard for the United States ending a seven-year-long search for a fully digital television standard. MPEG-2 was chosen as the video compression standard, and trellis-coded 8-vestigial sideband (VSB) with a training sequence was chosen as the transmission standard. The laboratory tests that were performed on the final two competing systems, 8-VSB with training sequence and 32-quadrature amplitude modulation (QAM) with blind equalization, showed a need for blind equalization in dynamic channels that could not be adequately handled by an equalizer training on the training sequence alone. Hence, the final GA system recommended the use of blind equalization in the receiver. In this paper, we describe the U.S. digital television transmission standard as it pertains to the equalization problem, typical transmission channel characteristics and the need for blind equalization in terrestrial television receivers 相似文献
17.
A new type of blind decision feedback equalizer (DFE) incorporating fixed lag smoothing is developed in this paper. The structure is motivated by the fact that if we make full use of the dependence of the observed data on a given transmitted symbol, delayed decisions may produce better estimates of that symbol. To this end, we use a hidden Markov model (HMM) suboptimal formulation that offers a good tradeoff between computational complexity and bit error rate (BER) performance. The proposed equalizer also provides estimates of the channel coefficients and operates adaptively (so that it can adapt to a fading channel for instance) by means of an online version of the expectation-maximization (EM) algorithm. The resulting equalizer structure takes the form of a linear feedback system including a quantizer, and hence, it is easily implemented. In fact, because of its feedback structure, the proposed equalizer shows some similarities with the well-known DFE. A full theoretical analysis of the initial version of the algorithm is not available, but a characterization of a simplified version is provided. We demonstrate that compared to the zero-forcing DFE (ZF-DFE), the algorithm yields many improvements. A large range of simulations on finite impulse response (FIR) channels and on typical fading GSM channel models illustrate the potential of the proposed equalizer 相似文献
18.
19.
20.
Concatenated coding schemes consist of the combination of two or more simple constituent encoders and interleavers. The parallel concatenation known as “turbo code” has been shown to yield remarkable coding gains close to theoretical limits, yet admitting a relatively simple iterative decoding technique. The recently proposed serial concatenation of interleaved codes may offer superior performance to that of turbo codes. In both coding schemes, the core of the iterative decoding structure is a soft-input soft-output (SISO) a posteriori probability (APP) module. In this letter, we describe the SISO APP module that updates the APP's corresponding to the input and the output bits, of a code, and show how to embed it into an iterative decoder for a new hybrid concatenation of three codes, to fully exploit the benefits of the proposed SISO APP module 相似文献