QR decomposition based M algorithm (QRD-M) is a type of maximum likelihood signal detecting (MLSD) scheme to provide a tradeoff detecting method between the system performance and complexity in multi-input multi-output (MIMO) communications. But for the conventional QRD-M algorithm, only one parameter, the maximum number of the survived branches, is used to make tradeoff, which cannot provide more valuable tradeoff options with better performance to complexity ratio. In this paper, an improved QRD-M algorithm with two independent parameters is proposed. It can provide more and better tradeoff options, which is proved through complexity analysis and numerical simulations.

Although frequency domain equalization (FDE) is very efficient to resist frequency selective fading in single-carrier communications, its performance will be greatly degraded due to high Doppler impact in a fast moving environment. To enhance the system performance of single-carrier communication system with FDE (SC-FDE), the self- cancellation technique is migrated from orthogonal frequency division multiplexing system (OFDM). It can obtain significant performance gain in scenarios with high Doppler in numerical simulations.

Constructing PCGCs with unequal-code-rate irregular component LDPC codes is proposed in this paper. Parameters of component codes are optimized by differential evolution based on EXIT chart. In the optimization results, code rate of component code 1 is relatively higher and the other one is lower so that these two component codes play different roles in different decoding stages. Numerical simulation results show that the proposed PCGCs with optimized parameters outperform PCGCs constructed by equal-code-rate regular/likely regular component codes and optimized irregular LDPC code.

A novel turbo codec with hybrid modulation is proposed in this paper. Instead of brutal puncturing, we apply different modulation alphabets to the original not-punctured turbo coded bits, where the systematic bits are modulated by a lower order constellation and the parity bits are mapped by a higher order constellation, respectively. Numerical results show that the proposed scheme without puncturing can noticeably improve the bit error rate (BER) and frame error rate (FER) performance of turbo codes in Rayleigh flat fading channels compared with the conventional turbo codes with puncturing and uniform modulation with the same spectral efficiency.

A novel adaptive LDPC coded OFDM transmission technique is proposed in this paper. Assuming the channel state information (CSI) is known to the transmitter, the irregular LDPC coded bits are ordered and allocated into subcarriers adaptively. Then two power allocation schemes, fixed ratio truncating (FRT) and fixed ratio inverse water-filling (FRIWF), are proposed to reallocate the power of each subcarrier. Performance of the strategy is analyzed by density evolution and numerical simulation. "Equal SNR search" (ESS) algorithm is also proposed to evaluate the performance of FRIWF scheme. Noticeable gain in terms of SNR can be achieved over frequency-selective fading channels.

Frequency domain equalization (FDE) is a very efficient way to resist frequency selective fading in single-carrier communications, but its performance will be greatly degraded when suffering serious Doppler impact due to time varying channel state. Based on the single-carrier system with FDE (SC-FDE), a segmentation FDE scheme is proposed to resist high Doppler in this paper without the price of system bandwidth efficiency. Through numerical simulations, its significant performance improvement in high Doppler is proved.

To enhance the bandwidth efficiency in cyclic prefix (CP) assisted OFDM system, we propose a complexity reduced blind channel equalization scheme based on the finite alphabet property of the transmitted signal and we also present its simplification scheme in this paper. According to the numerical simulation results, our proposals can perform as well as the conventional pilot assisted frequency domain channel estimation (PFDCE) in high Eb/N0, but a little worse in low Eb/N0

Cyclic Prefix (CP) has been applied in the single-carrier systems to resist the inter-block interference (IBI) due to the frequency selective fading channel and equalize the channel by one-tap frequency domain equalizer. However, there still exists the residual inter-symbol interference (ISI) due to imperfect channel equalization, which will severely degrade the system performance. In this paper the residual ISI is analysis in CP-SC with linear minimum mean square error (LMMSE) equalizer. With the initial estimates of LMMSE equalizer, the interference cancellation (IC) technique is adopted to alleviate the residual ISI so that the system performance can be considerably improved.

In general, cyclic prefix (CP), zero padding (ZP) or fixed symbol padding (FP) can be seen as the guard interval (GI) for data transmitting. By inserting enough long GI, we can remove inter-block interference (IBI) completely, and the signal distortion due to multi-path environment can be simply compensated by frequency domain equalization (FDE). But on the other hand, the system bandwidth efficiency will be decreased due to the redundancy of GI and additional channel estimation pilots. This paper proposes a new scheme to estimate channel state with the help of our special type GI and presents the FDE scheme based on the proposed GI system

The adaptive frequency domain interference cancellation and channel equalizer for MIMO-CP-CDMA systems is proposed to cancel the residual interference stage by stage. At each stage, the proposed scheme performs the adaptive forward filtering and interference cancellation in frequency domain so that the signal to interference plus noise ratio can be improved and the error propagation of the interference cancellation can be avoided. The achieved SINR of each code channel is utilized to compute the normalized correlation coefficient. Simulation results show that the proposed scheme can achieve the satisfactory performance and avoid the error propagation

High peak-to-average power ratio (PAPR) is an inherit drawback of orthogonal frequency-division multiplexing (OFDM) systems, and it limits the use of OFDM technology. In all the PAPR reduction methods, digital clipping is probably the simplest one and it is very effective in the solution of the PAPR problem in OFDM systems. However, clipping introduces additional distortion, which degrades the performance of channel estimation and signal detection. In this paper, the performance of channel estimation using the simple least square (LS) method in OFDM systems with a clipping operation is analyzed, a decision-aided channel estimation method to mitigate the clipping distortion is developed, and the potential gain in channel estimation of the decision-aided method is derived theoretically. Simulation results show that, in clipped OFDM, the theoretical potential gain in channel estimation can be obtained by a few iterations of an iterative decision-aided channel estimation and signal detection process, and, simultaneously, the performance of signal detection is effectively improved

This paper considers the design of iterative receivers for space-frequency block-coded orthogonal frequency division multiplexing (SFBC-OFDM) systems in unknown wireless dispersive fading channel with outer channel coding. The iterative joint channel estimation and symbol detection algorithm is derived. A simple decision-error judgment criterion is proposed and an improved training scheme is applied in the system to suppress the error propagation. Both theoretical analysis and computer simulation show that this algorithm gives better BER performance and saves the overhead of OFDM systems

When MIMO channel correlation information is available at the transmitter, closed-loop precoding can be introduced to improve system performance. In this paper, we proposed a novel closed-loop precoding algorithm based on code distance allocation for transmit correlated spatial multiplexing MIMO systems. We show that pairwise error probability of transmit correlated spatial multiplexing MIMO systems is determined by the minimum transmit code distance allocated to each eigenmode subchannel. We give the structure of code distance allocation matrix to optimize transmit code distance. Our proposed structure of code distance allocation matrix can simultaneously optimize minimum code distance allocated to each subchannel. Computer simulations show that our proposed procoding algorithm can improve the performance of transmit correlated spatial multiplexing systems

Bell Lab vertical layered space-time architecture (V-BLAST) is an approach for exploiting high MIMO channel capacity. A power allocation algorithm has been proposed to improve bit error rate performance when using ordering successive interference cancellation (OSIC) detection. However, the BER performance of proposed power allocation algorithm degrades greatly with the increase of transmit antenna correlation. In this paper, we proposed a closed-loop precoding algorithm based on OSIC detection. Our proposed precoding algorithm combines decorrelation with power allocation algorithm to improve the BER performance of transmit correlated V-BLAST systems. Computer simulations demonstrated that our proposed precoding method has better performance than mere power allocation algorithm

OFDM symbols exhibit a property of high peak-to-average power ratios (PAPR), which degrades system performance. Partial transmit sequence (PTS) is a kind of methods to depress the PAPR effectively. To obtain good trade-offs between complexity and performance on PAPR reduction using PTS schemes, a trellis structure based PTS factor search method is proposed and investigated in this paper. The trellis search is with a variant constraint length L/sub C/, 1/spl les/L/sub C//spl les/V-1, where V is the number of PTS sub-blocks. The method is to decide a PTS factor by searching all possible paths obtained by varying L/sub C/ consecutive factors. Using different constraint length, trellis factor search PTS exhibits different PAPR reduction performance with different computation burden. The trellis search can be viewed as a general PTS factor search model including the full search and the iterative search appeared in previous papers.

In this paper, effects of cyclic prefix (CP) are investigated for orthogonal frequency division multiplexing (OFDM) systems over time-varying channels. Although employing a CP as the guard interval is a simple way to combat the inter-symbol interference (ISI) and the inter-carrier interference (ICI), it reduces the transmission efficiency of the system, especially for channels with long channel-impulse response (CIR), such as hilly terrain channels. On the other hand, the time-varying channel also gives rise to ICI. We show that to achieve a signal-to-interference ratio of 20 dB, for slow fading channels, half the length of CIR is enough for CP. For fast fading channels, the Doppler frequency become domination factor to affect OFDM systems

Orthogonal frequency division multiplexing (OFDM) is the projected modulation of choice for fourth-generation broadband multimedia wireless systems. However, for mobile applications, channel variations during one OFDM symbol introduce intercarrier interference (ICI), which degrades the performance. This gets more severe as mobile speed, carrier frequency or OFDM symbol duration increases. In this paper, we first analyze the ICI caused by time-variant channel in terms of the complex weighting coefficients, which give the contribution of each transmitter subcarrier to each demodulated subcarrier. Then, we propose a high efficiency intercarrier interference cancellation scheme to reduce the effects of Doppler frequency shift. Finally we derive the signal-to interference power ratio (SIR) for the proposed OFDM system. From the comparison between the normal OFDM and the proposed system, we can see that such an ICI cancellation scheme gives more than 5 dB SIR improvement. The simulation results confirm the analysis and show the SIR improvement.

We investigate the difference between extrinsic and posteriori information fed back from outer decoder to inner detector in a turbo-BLAST system for a quasistatic channel. With the help of extrinsic information transfer (EXIT) chart and simulation, it is observed that a faster convergence rate is obtained to feed back posteriori information, and especially, a better steady state performance is attained when antenna number is small.

Clipping is a popular method to overcome large peak-to-mean envelope power ratios (PMEPRs) in orthogonal frequency-division multiplexing (OFDM) systems, but it results in nonlinear distortion, which degrades signal detection performance. In this paper, clipping effects on signal detection with a simple channel estimation in OFDM are investigated, signal-to-noise and distortion ratio (SNDR) results of detected signals are derived, and symbol error rates (SERs) of clipped OFDM in frequency selective Rayleigh fading channels are evaluated. The evaluated SER results are supported by simulations.

The use of multiple antennas at the transmitter and receiver results in enormous capacity increase. As a space-time architecture, VBLAST (vertical Bell laboratories layered space time) has demonstrated very high spectral efficiency. Originally, the BLAST detection scheme, called OSIC (ordered successive interference cancellation), was based on a successive interference cancellation. OSIC suffers from the error propagation problem. In this paper, we present a modified detection algorithm, called PD/spl I.bar/OSIC (partial decision OSIC), which aims at improving the performance of OSIC. It increases the number of candidate symbols, remains all candidate symbols and uses ML detection to detect all substreams at last stage. The simulation results show that the proposed algorithm obtains far better performance than OSIC.

An improved channel estimator with inter-symbol interference (ISI) free window measurement for OFDM systems is proposed by exploiting the inherent correlation between the cyclic prefix and portion of the received OFDM signal. This scheme make use of real time measured size of ISI free window to estimate the maximum delay spread of channel, then a transform domain channel estimator is adopted to further reduce the noise variance. Due to the ISI-free window can be estimated before the application of FFT to the received signal, it is a parallel processing, and very suitable for practical systems. Simulation result demonstrated that the proposed method can track the variation of delay spread of wireless channel, and improve the MSE of channel estimation significantly, thus give at least 1-db improvement in TU channel and 0.5-db in HT channel.

Multiple-input multiple-out (MIMO) wireless transmission has been proved to be a promising technique to support high data rate transmission. Among proposed schemes, space-time codes are designed to improve transmission reliability, while BLAST architectures are proposed to improve spectrum efficiency. To optimize both channel capacity and error probability, linear dispersion codes (LDCs) were proposed. However, original LDCs are designed for quasi-static fading channels, which don't guarantee optimal error probability in fast fading channels. In this paper, we discuss performance of LDCs both in quasi-static and fast fading channels. And we propose a modified LDCs transmission scheme, in which we introduce an interleaver in each antenna branch to turn quasi-static channels into equivalent fast fading channels. Then we present codes optimization criterion to search for LDCs which optimal both in quasi-static and fast fading channels. Computer simulations show that the performance of proposed LDCs design method is better than original LDCs.

Abstract Three design requirements of space‐time block code, full diversity order, full data rate and orthogonality, cannot be achieved simultaneously when the number of transmit antenna is more than two. In this paper, we propose a transmit diversity scheme—circular shifted transmit diversity (CSTD). CSTD can always achieve the full data rate and has very low decoding complexity. Through the performance analysis and simulation comparison in the case of same spectrum efficiency between CSTD and other well‐known proposed schemes, it can be proved that CSTD always significantly outperforms the other transmit diversity schemes with full data rate. Additionally, compared with the transmit diversity schemes with full diversity order, CSTD has lower complexity and approximately the same performance when channel coding is concatenated. Copyright © 2004 John Wiley & Sons, Ltd.

Space-time transmission techniques, which make full use of the rich scattering channel with multiple transmit and receive antennas, can greatly increase the spectral efficiency. The conventional V-BLAST (Bell laboratories layered space-time) detection algorithm estimate symbols with the expected SNRs ordering. In this paper, a novel BLAST detection algorithm based instantaneous error ordering (IEO-BLAST) is proposed. The proposed BLAST detection algorithm obtains the additional diversity with instantaneous error ordering and reduces the effect of the error propagation. Therefore, the performance of the BLAST architecture is greatly improved. In addition, the simplified version of IEO-BLAST detection algorithm (SIEO-BLAST) is derived. And the performance of simplified algorithm has little degradation. The selection capacity (SC) is defined to represent the performance of the algorithm with successive interference cancellation.

In BLAST (Bell lab's layered space time) systems, very high spectral efficiency can be achieved by employing antenna array at both transmitter and receiver sides. Coding for such a system is an interesting topic. In this paper, we further study the detection and decoding performance with horizontal coding structure. Our main interest is in the performance and complexity trade-offs involved in the design of coding/decoding and signal detection algorithms. We show that unequal protection capability codes may be used in different layers to improve the BLER (block error rate) without additional complexity. Simulation results show that the same performance as hard-decision iterative detection is obtained. Furthermore, through a CRC (cyclic redundancy check), the sphere decoding is used to refine the detection result. Therefore, the performance is significantly improved with affordable computational complexity.

It is well known that space-time block code with full diversity and full data rate is not possible for more than two transmit antennas. In this paper, space-time transmit diversity with antenna hopping (STTD-AH) is proposed to achieve full data rate and orthogonality for three transmit antennas. In the case of same spectrum efficiency, STTD-AH always significantly outperforms the other transmit diversity schemes and has very low decoding complexity. Additionally, because of the spatial interleaving formed in STTD-AH, the performance loss due to the reduced diversity order can be compensated by concatenating forward error correction coding.

Clipping is a popular and simple method to overcome large peak to mean envelope power ratio (PMEPR) in OKDM system, but it results in a nonlinear distortion, which degrade the performance of channel estimation and signal detection. In this paper we estimated OFDM channel using a simple LS method based on a scheme that only part of the OFDM tones arc used for pilot, in which the clipping distortion is unknown for the receiver, and then we analyze the clipping effects on channel estimation. According to the estimated channel, we detected the OFDM signal and analyze the clipping effects on signal detection. We derived the BER solution of clipping OFDM in Rayleigh fading channel and the numerical solution is very close to simulation results.

Space-time transmission techniques, which make full use of the rich scattering channel with multiple transmit and receive antennas, can greatly increase the spectral efficiency. In this paper, a novel parallel multistage equalizer with partial decision feedback (PDF) is proposed for the layered space-time frequency-selective channel. It is comprised of a partial parallel interference canceller, a MIMO decision feedback equalizer and a linear combiner. Performance analysis shows that the proposed receiver is equivalent to the partial parallel interference cancellation (PPIC) using MMSE for initial estimation and tentative decisions. By using past- and post-symbol estimation to regenerate intersymbol and co-antenna interference, the proposed receiver can be further improved with partial decision feedback. Moreover, the proposed equalization schemes could be implemented by negligible complexity increase comparing with the other well-known approaches. Simulation results show that the proposed equalizers with PDF significantly outperform the conventional MIMO decision feedback equalizer without interference cancellation (IC) and MIMO equalizer with ordering successive interference cancellation (OSIC).

Space-time transmission techniques, which make full use of the rich scattering channel with multiple transmit and receive antennas, can greatly increase the spectral efficiency. In this paper, parallel multistage decision feedback equalizer (DFE), which is composed of parallel interference cancellation, multiple input single output decision feedback equalizer (MISO-DFE) and linear combination of the soft outputs of MISO-DFE and the previous soft decisions, is proposed for a single-carrier system over layered space-time frequency-selective channels. In addition, an algorithm is proposed to obtain the soft and hard decisions for initialization. And the proposed parallel multistage DFE can be implemented with lower complexity than MIMO-OFDM. Simulation results show that the parallel multistage DFE outperforms the MIMO-OFDM and various previous equalizers for a single-carrier system.

In this paper, two kinds of space-time block coded transmit diversity are proposed for OFDM system in mobile channels. One is in time domain and at least one frame (one symbol) delay is needed for the decoding algorithm; the other is in frequency domain so it also can be termed as space-frequency coded (SFC) transmit diversity more concisely, and no delay is needed for the decoding algorithm. We simulate the performance of these kinds of space-time block coded transmit diversity, the space-time trellis coded transmit diversity with 4- and 16-state are also simulated to give out a performance comparison with space-time block coded transmit diversity in this paper.

The Gauss-Seidel iterative algorithm for linear asynchronous decorrelation or minimum mean square error (MMSE) multiuser detector can be viewed as a kind of linear soft decision feedback multiuser detection. Based on this idea, a linear decorrelating or MMSE detector can be implemented by using a much simpler pipeline structure compared with the conventional scheme of computing the inverse of the corresponding correlation matrix. Through this pipeline structure, a lot of computations can be reduced.

The effects of fading channels and multiple access interference limit the performance of downlink WCDMA systems. In this paper, a linear minimum mean-square error multiuser receiver with space-time transmit diversity is proposed for downlink WCDMA systems. The fading effect and multiple access interference can be jointly mitigated by the proposed scheme. The performance analysis under Gaussian approximation has also been carried out. Simulation results show that substantial performance gain can be achieved compared with conventional algorithms.

Multicode CDMA with V-BLAST architecture is an attractive scheme to achieve high data rate transmission. We propose an advanced detection scheme, order partial parallel interference cancellation with decision feedback (DF-OPPIC), to combat co-antenna interference and multiple access interference in the system. Compared with conventional V-BLAST detection algorithms, the scheme has better performance on the frame error ratio in flat Rayleigh fading channel and multipath Rayleigh fading channel. Moreover, due to avoiding calculating pseudo-inverse and optimal detection order at every time of iteration, the scheme has lower arithmetic complexity.

Multicode CDMA with V-BLAST architecture is an attractive scheme to achieve high data rate transmission. We propose an advanced detection scheme, order partial parallel interference cancellation with decision feedback (DF-OPPIC), to combat co-antenna interference and multiple access interference in the system. Compared with the original reference, the scheme has better performance on the frame error ratio in flat Rayleigh fading channel and multipath Rayleigh fading channel. Moreover, due to the avoidance of calculating pseudo-inverse and optimal detection order in every time of iteration, the scheme has lower arithmetic complexity.

A novel realization scheme of space-time block code (STBC) is proposed by unequal power distribution between different transmitting (Tx) antennas at slow fading scenario. With optimal power distribution between the Tx antennas, the scheme can achieve a better performance than conventional STBC with equal transmitted power. Then we analyze and simulate the performance difference.

Energy efficiency is an important issue for mobile devices in ad hoc networks since they often have to rely on their batteries. In consideration that current mesh-based multicast routing protocols don't tend to form energy-efficient multicast infrastructure, we propose a new energy-efficient multicast routing protocol (E/sup 2/MRP) for mobile ad hoc networks. The two main characteristics of E/sup 2/MRP are 1) using in turn the criteria for minimum energy consumed per packet and minimum maximum node cost during the course of relaying group (RG) creation and maintenance, and 2) forming a graph-based multicast infrastructure instead of a tree-based one. For comparison, E/sup 2/MRP is implemented together with multicast incremental power (MIP) protocol and on-demand multicast routing protocol (ODMRP). When over half of nodes join multicast group and nodes move at higher speed, as we observe, MIP results in higher energy consumption for each packet than E/sup 2/MRP and ODMRP due to the fragile multicast tree. Compared to MIP and ODMRP, E/sup 2/MRP tremendously reduces the energy consumption rate of nodes and hence prolongs the lifetime of nodes and networks, especially when the size of multicast group is small and node mobility is low. Simulation results demonstrate significant performance improvement.

The purpose of ATM is to provide a high-speed, low-delay multiplexing and switching network to support any type of user traffic. It has not achieved this goal after 10 years of implementation. The reason may be various, but the fatal one is its low efficiency when supporting data traffic. Upgrading is the only way that ATM could keep its existence. We propose a novel architecture to improve the current ATM performance. By defining a new cell structure, the new ATM reinforces the end-to-end error control ability, and greatly increases the data transmission efficiency. The introduction of the micro cell further enhances its ability to support a low-speed real-time service. The new architecture can also support bi-directional point-to-multi-point transmission and can be used in the wireless environment directly. To verify its applicability, various simulations are carried out. We introduce our simulation tests on CBR transmission delay, Web response delay, sustained data transfer rate, and link utilization. The analysis and simulation show that, such a modification can overcome the shortcoming of the existing ATM protocol and upgrade its ability to support more services effectively.

Two bit estimators, the weighted average bit estimator and shrinkage bit estimator, used in DS-CDMA partial parallel interference cancellation (PPIC) proposed by Divsalar et al. (see IEEE Trans. on Comm., vol.46, no.2, 1998) , are compared. It is shown that the two bit estimators improve the performances by decreasing the power of the residual interferences, remaining in the decision statistic of each stage after interference cancellation, but in different capabilities. We also justify the assumption that the residual interference is Gaussian, under which the two bit estimators are derived by Divsalar et al. Furthermore, theoretical optimal weights of the above two estimators minimizing the BER are derived.

We use a simulation method to analyze the performance of TCP Reno, NewReno, SACK and Vegas in wireless ad hoc networks. We propose an alternative adapted SACK option format (ASACK) and a new technique, round trip time (RTT) notification (RN), to improve the performance of TCP Reno and Vegas in wireless ad hoc networks respectively. An associativity-based routing (ABR) protocol is also implemented to study how the route stability affects the performance of TCP.

The performance comparison and analysis between space-time trellis code (STTC) and space-time block code (STBC) is given. It is observed that the 2STBC scheme has a fixed performance, while in contrast the 2STTC can improve its performance by increasing states. Furthermore, we prove that coding advantage is not always reliable for analyzing the performance of a space-time code (STC).

A reduced complexity multistage detector is introduced for DS-CDMA systems, which is derived from the soft sigmoid decision PIC (parallel interference cancellation) detector. From the derivation, we can see that this reduced complexity detector has a clear partial interference cancellation explanation about the soft sigmoid PIC detector. Derivation and computer simulations show that the proposed detector can reach the performance of the soft sigmoid PIC detector easily without the variance estimation of the residual noise at each stage or the sigmoid decision function which is not easily implemented in practice.

Space-time spreading (STS) is considered as one of the transmit diversity schemes in the current cdma2000 standard. Space-time transmit diversity (STTD) has been proposed and specified in WCDMA standardization. In this paper, the performance of STS and STTD have been evaluated and compared in forward link CDMA2000 systems. The performance analysis and simulation results show that these two schemes have approximately the same performance on the frame error ratio in multipath fading channels even with imperfect channel estimation. But STS has more implementation complexity and higher peak to average ratio compared with STTD.

Space-time trellis codes can achieve the best tradeoff between bandwidth efficiency, diversity gain, constellation size and trellis complexity. We propose some optimum low rate space-time trellis codes. Performance analysis and simulation show that the low rate space-time trellis codes outperform space-time block codes concatenated with convolutional code at the same bandwidth efficiency, and is more suitable for the power limited wireless communication system.

In this paper, a multiuser receiver, which cancels the multiple access interference (MAI) of the stage-based fractional number of users, is proposed for CDMA systems. In each stage, MAI of fractional number of users is regenerated and subtracted from the received signal. The fractional number is defined according to the number of successive stages. The simulation results show that the performance can be significantly improved by the proposed scheme compared to the conventional multistage detector.

We propose the application of a modified transiently chaotic neural network to solve the optimum detection problem in DS/CDMA systems. The optimum detection problem is formulated as an energy minimization problem. It can be minimized by a modified transiently chaotic neural network (MTCNN). The MTCNN-based detector offers performance improvement over the existing Hopfield neural network detector with a little increase in computational complexity. Numerical results show that the proposed detector can approximate the optimum detector closely.

This paper presents a new ABR flow control scheme using explicit rate information in backward RM cells. Recording to this scheme, a network can dynamically allocate bandwidth resource by using the global information called the loadlevel of the network. It's much faster for all the ABR sources in the network to reach their optimal rates. The available bit rates the ABR sources obtain go up from their minimal fairshares to their maximal fairshares monotonously. In this sense the scheme is oscillation avoid.

The complex algorithm of the sliding exponential window recursive least-squares (SEWRLS) algorithm and its square-root method's DFE for a time division multiple access (TDMA) digital cellular system are treated in this paper. First, we derive two complex algorithm structures of the SEWRLS and present its square-root factorization algorithm. Then their applications in fast-varying systems are discussed.

It has been observed by many authors that the backpropagation (BP) error surfaces usually consist of a large amount of flat regions as well as extremely steep regions. As such, the BP algorithm with a fixed learning rate will have low efficiency. This paper considers dynamic learning rate optimization of the BP algorithm using derivative information. An efficient method of deriving the first and second derivatives of the objective function with respect to the learning rate is explored, which does not involve explicit calculation of second-order derivatives in weight space, but rather uses the information gathered from the forward and backward propagation, Several learning rate optimization approaches are subsequently established based on linear expansion of the actual outputs and line searches with acceptable descent value and Newton-like methods, respectively. Simultaneous determination of the optimal learning rate and momentum is also introduced by showing the equivalence between the momentum version BP and the conjugate gradient method. Since these approaches are constructed by simple manipulations of the obtained derivatives, the computational and storage burden scale with the network size exactly like the standard BP algorithm, and the convergence of the BP algorithm is accelerated with in a remarkable reduction (typically by factor 10 to 50, depending upon network architectures and applications) in the running time for the overall learning process. Numerous computer simulation results are provided to support the present approaches.

A new scheme, called pre-decorrelating strategy, is proposed for single user detection in the forward direction of centralized DS-CDMA systems. The basic idea is that, instead of the data themselves, the linear combinations of active users' data are transmitted, which can then decorrelate the cross-correlation between users at the receiver. In the flat Rayleigh fading environment, analysis and simulations show that the receiver is much simplified and can well cancel the multiple access interference regardless of the interference powers and without any knowledge of other users' signature waveforms.

This paper introduces a new scheme for single user detection in the forward direction of centralized DS/CDMA systems. The basic idea is that, instead of the data themselves, the linear combinations of active users' data according to the inverse crosscorrelation matrix of their signature waveforms are transmitted. With the proposed scheme, the simple correlator can well cancel the multiple access interference like the decorrelating multiuser detector while the signature waveforms of other users do not need to be known at the receiver. Analysis and simulation results of the performance are presented.>

Investigates the performance of direct-sequence spread-spectrum packet radio networks in the presence of the near/far problem. It is found that the maximum throughput of the network suffers degradation due to the near/far problem. However, analysis also shows that, under high traffic conditions, a network with the near/far problem delivers higher throughput than another without the near/far problem. This suggests that the direct-sequence spread-spectrum packet radio network with the near/far problem retains stability for heavier traffic conditions. Following these findings, a new adaptive power control scheme is suggested to enhance network throughput under both low and heavy traffic conditions. The mean and variance of the packet delay are derived and network stability and deadlock avoidance issues are discussed. The impact of channel fading on the network behavior is also studied.>