Interference mitigation using transmitter filters in CDMA systems

We consider the use of transmitter filters as pre-equalizers at the base station to mitigate the interference in code-division multiple-access (CDMA) systems over a multipath fading channel. It is shown that the interference at the receiver of the mobile station can be mitigated by the transmitter filters and, thereby, the capacity of downlink channel can be improved. The minimum variance distortionless response (MVDR) beamforming technique in antenna arrays has been utilized to find the coefficients of the interference mitigation (IM) transmitter filters. To design IM transmitter filters, we assume that the channel information is available. This can be true in the time-division duplexing (TDD) mode because of the channel reciprocity. In the frequency-division duplexing mode, the downlink channel impulse responses (CIRs) shall be be transmitted to the base station. To transmit the CIRs, we consider an encoding method. In addition, to compensate inherent feedback delay, the channel prediction is also utilized     

Joint optimization of transmitter and receiver filters in digital PAM systems with a Viterbi detector

Joint optimization of transmitter and receiver filters in a pulse-amplitude modulation (PALM) system with an arbitrary but fixed Viterbi detector is considered. Optimization is performed under an average transmitted power constraint with respect to a new criterion called the effective mean-square error (EMSE). It is shown that the optimization problem is convex. A necessary and sufficient condition for optimality is derived, and a method for optimization is proposed. Numerical results are obtained for a channel with coaxial cable characteristics.     

Jointly minimum BER transmitter and receiver FIR MIMO filters for binary signal vectors

A theory is developed for jointly minimizing the bit error rate (BER) between the desired and decoded signals with respect to the coefficients of transmitter and receiver finite impulse response (FIR) multiple-input multiple-output (MIMO) filters. The original signal is assumed to be a vector time-series with equally likely memoryless Bernoulli vector components. The channel model constitutes of a known FIR MIMO transfer function and Gaussian additive noise independent of the original signal. The channel input signal is assumed to be power constrained. Based on the formulas obtained, an iterative numerical optimization algorithm is proposed. When compared with other design methods available in the literature, the proposed method yields better results due to the generality of the model considered and the joint optimization of the transmitter-receiver pair.     

Design and analysis of receiver filters for multiple chip-rateDS-CDMA systems

As multimedia applications proliferate, there is a desire to provide wireless transport to information streams with inherently different data rates. Direct-sequence code division multiple access (DS-CDMA) is a natural multiple-access strategy for multiple data-rate systems. Previous work on multirate DS-CDMA receivers has focused on signal-processing techniques, which detect all users of all rates simultaneously. In the current work, multirate users have multiple bandwidths. Thus, it is proposed to exploit bandwidth differences to achieve frequency-based rate separation followed by single-rate detection schemes. Such a methodology enables a tradeoff between receiver complexity and performance. The performance of the proposed filters and receivers are derived for both a modified matched filter and modified decorrelator employing rate separation. The performance of a multirate CDMA overlay system is evaluated. In addition, chip pulse shaping for wide-band users is developed to improve performance for narrow-band users for the overlay system     

Joint linear transmitter and receiver design for the downlink of multiuser MIMO systems

In this letter, we address the problem of designing jointly the linear transmitter and receiver for the downlink of Multiuser MIMO system, using minimum total mean square error criterion (T-MMSE), subject to a total transmit power constraint. We show that transmitter and receiver under such criterion could be realized through a joint iterative algorithm. The convergence of the proposed algorithm is proved. Simulation results have also been provided to demonstrate the feasibility of this new method.     

Capacity of multiple-antenna systems with both receiver and transmitter channel state information

The capacity of multiple-antenna systems operating in Rayleigh flat fading is considered under the assumptions that channel state information (CSI) is available at both transmitter and receiver, and that the transmitter is subjected to an average power constraint. First, the capacity of such systems is derived for the special case of multiple transmit antennas and a single receive antenna. The optimal power-allocation scheme for such a system is shown to be a water-filling algorithm, and the corresponding capacity is seen to be the same as that of a system having multiple receive antennas (with a single transmitter antenna) whose outputs are combined via maximal ratio combining. A suboptimal adaptive transmission technique that transmits only over the antenna having the best channel is also proposed for this special case. It is shown that the capacity of such a system under the proposed suboptimal adaptive transmission scheme is the same as the capacity of a system having multiple receiver antennas (with a single transmitter antenna) combined via selection combining. Next, the capacity of a general system of multiple transmitter and receiver antennas is derived together with an equation that determines the cutoff value for such a system. The optimal power allocation scheme for such a multiple-antenna system is given by a matrix water-filling algorithm. In order to eliminate the need for cumbersome numerical techniques in solving the cutoff equation, approximate expressions for the cutoff transmission value are also provided. It is shown that, compared to the case in which there is only receiver CSI, large capacity gains are available with optimal power and rate adaptation schemes. The increased capacity is shown to come at the price of channel outage, and bounds are derived for this outage probability.     

Iterative transmitter and receiver optimization for CDMA networks

Optimization of the capacity of a single-cell code-division multiple-access (CDMA) system, both from the perspective of the maximum number of users that can be served at a required quality of service level and from the information theoretic perspective, has been recently shown to be achieved by the same joint transmit and receive strategies. We propose an alternating minimization based iterative algorithm that updates the transmitters and the corresponding receivers of the users. The algorithm is suitable for online implementation, and the objective function is suitable for extension to multicell networks, both of which are in contrast with the previously proposed algorithms. We show that the algorithm is provably convergent to the optimum signature sequences and the corresponding receivers.     

On joint transmitter and receiver optimization formultiple-input-multiple-output (MIMO) transmission systems

The problem of joint transmitter and receiver optimization for MIMO systems under the mean-squared error (MSE) criterion is revisited. We address the general problem of N (number of users) ≠M (number of channel inputs) ≠P (number of channel outputs) when the system is Nyquist bandlimited and obtain analytical solutions for the optimal transmit-receive pair. Next, we demonstrate how the above result is directly applicable to the problem where the system has excess bandwidth, thereby generalizing the results of Salz (1985). In conclusion, several numerical examples are included to demonstrate the performance gains obtainable with jointly optimized MIMO systems vis-a-vis systems based only on receiver optimization     

Error performance of optically preamplified hybrid BPSK-PPM systems with transmitter and receiver imperfections

In this paper, we investigate the impact of the transmitter finite extinction ratio and the receiver carrier recovery phase offset on the error performance of two optically preamplified hybrid M-ary pulse position modulation (PPM) systems with coherent detection. The first system, referred to as PB-mPPM, combines polarization division multiplexing (PDM) with binary phase-shift keying and M-ary PPM, and the other system, referred to as PQ-mPPM, combines PDM with quadrature phase-shift keying and M-ary PPM. We provide new expressions for the probability of bit error for PB-mPPM and PQ-mPPM under finite extinction ratios and phase offset. The extinction ratio study indicates that the coherent systems PB-mPPM and PQ-mPPM outperform the direct-detection ones. It also shows that at \(P_b=10^{-9}\) PB-mPPM has a slight advantage over PQ-mPPM. For example, for a symbol size \(M=16\) and extinction ratio \(r=30\) dB, PB-mPPM requires 0.6 dB less SNR per bit than PQ-mPPM to achieve \(P_b=10^{-9}\). This investigation demonstrates that PB-mPPM is less complex and less sensitive to the variations of the offset angle \(\theta \) than PQ-mPPM. For instance, for \(M=16\), \(r=30\) dB, and \(\theta =10^{\circ }\) PB-mPPM requires 1.6 dB less than PQ-mPPM to achieve \(P_b=10^{-9}\). However, PB-mPPM enhanced robustness to phase offset comes at the expense of a reduced bandwidth efficiency when compared to PQ-mPPM. For example, for \(M=2\) its bandwidth efficiency is 60 % that of PQ-mPPM and \(\approx 86\,\%\) for \(M=1024\). For these reasons, PB-mPPM can be considered a reasonable design trade-off for M-ary PPM systems.     

用于计算机光互连的集成化发送器和接收器

从对计算机光互连的实用要求出发，实现了用集成化的发送器和接收器经光纤连接器组成收发对后，能很好地在４×４多处理机系统内用光互连代替电互连。着重探讨了发送器和接收器的结构、设计，以及工艺改进途径，对互连器件的配套选择、性能测试作了一定工作，使之能方便使用。     

高速多带NGI-OOFDM传输系统中的非对称发射机与接收机设计

在高速多带无保护间隔(NGI)光正交频分复用(OOFD M)传输系 统中,采用非对称发射机/接收机结构,对接收信号通过多个通用光相干接收机进行部分探 测,可一次完整 接收整个多带NGI-OOFDM信号。发射端采用单个激光源,通过差分马赫曾德尔外调制器产生 8根等频率 间隔为28GHz的光频梳作为光子载波,经112 Gbit/s PDM-QPSK信号调制,波分复用后形成8路宽带的全 光NGI-OOFDM信号。接收端采用非对称发射机/接收机结构,即采用4个接收带宽为 18GHz的通用光相 干接收机,每个接收机接收2路子载波,可以完整接收整个多带NGI-OOFDM信号。采用本文 结构的高速多 带NGI-OOFDM传输系统,误码率(BER)为10－3时, 光信噪比(OSNR)代价较单载波112Gbit/s PDM-QPSK系 统多约9dB。 经16,0ps/nm光纤色散及偏振扰动,在系统接收端通过电色散补偿 后,约有 0.2dB OSNR代价。最后 对传输13×80km的光纤链路进行了仿真,仿真结果表明,与背靠背 情况相比,在进行电色散补偿后,OSNR代价约1.5dB。     

A mean field approach for simulating wavelength-divisionmultiplexed systems

We simulated many-channel, wavelength-division-multiplexed optical fiber transmission systems by following the full time-domain evolution for only a few channels around a target channel, white treating the rest of the channels as continuous-wave radiation. We show a good agreement between our approach and full numerical simulations. By using our approach, one can greatly reduce the computation time compared with full simulations     

Channel estimation in the presence of transmitter and receiver I/Q mismatches for OFDM systems

In this paper, we study the problem of channel estimation in the presence of the transmitter and receiver inphase and quadrature-phase (I/Q) mismatches for orthogonality frequency division multiplexing (OFDM) systems. A new concept called channel residual energy (CRE) is introduced. We show that by minimizing CRE, we can jointly estimate the transmitter and receiver I/Q mismatches without knowing the channel information. The optimal solution is given in closed form. Once we have the I/Q parameters, an estimate of the channel response can be obtained by simple substitution. The proposed method needs only one OFDM block for training and the training data can be arbitrary. Simulation results show that the proposed method can achieve a good performance.     

Joint transmitter receiver diversity for efficient space divisionmultiaccess

The beamforming problem is studied in wireless networks where both the transmitters and receivers have linear adaptive antenna arrays. Algorithms are proposed that find the antenna array weight vectors at both the transmitters and receivers as well as the transmitter powers with one of the following two objectives: (1) to maximize the minimum signal-to-interference-and-noise ratio (SINR) over all receivers and (2) to minimize the sum of the total transmitted power satisfying the SINR requirements at all links. A numerical study is performed to compare the network capacity and the power consumption among systems having a different number of antenna array elements in a code division multiple access network     

Novel receiver structures for systems using differential detection

Novel receiver structures are introduced which improve the bit error rate performance of differentially detected MSK and QPSK systems. These new receiver structures are based on 1) combining with feedback, 2) a simple Viterbi decoder which uses one- and two-bit detector outputs for maximum-likelihood sequence estimation, and 3) using the correlation of noise for the partial removal of its effect prior to decision. The new receiver structures presented are useful in mobile radio and mobile satellite communications where power efficiency, synchronization, and implementation complexity are of primary concern.     

Image and video compression algorithms based on recovery techniquesusing mean field annealing

Image and video coding algorithms have found a number of applications ranging from video telephony on the public switched telephone networks (PSTN) to HDTV. However, as the bit rate is lowered, most of the existing techniques, as well as current standards, such as JPEG, H. 261, and MPEG-1 produce highly visible degradations in the reconstructed images primarily due to the information loss caused by the quantization process. In this paper, we propose an iterative technique to reduce the unwanted degradations, such as blocking and mosquito artifacts while keeping the necessary detail present in the original image. The proposed technique makes use of a priori information about the original image through a nonstationary Gauss-Markov model. Utilizing this model, a maximum a posteriori (MAP) estimate is obtained iteratively using mean field annealing. The fidelity to the data is preserved by projecting the image onto a constraint set defined by the quantizer at each iteration. The proposed solution represents an implementation of a paradigm we advocate, according to which the decoder is not simply undoing the operations performed by the encoder, but instead it solves an estimation problem based on the available bitstream and any prior knowledge about the source image. The performance of the proposed algorithm was tested on a JPEG, as well as on an H.261-type video codec. It is shown to be effective in removing the coding artifacts present in low bit rate compression     

Synchronized etalon filters for standardizing WDM transmitter laserwavelengths

The authors report a simple technique to synchronize solid etalons which provides identical sets of equally spaced absolute reference frequencies. To demonstrate the principle, 1-mm-thick fused silica etalons were synchronized to have identical sets of resonant frequencies at 195.579±n×0.1034 THz, where n is any integer. These references were temperature-insensitive with the aid of a temperature control loop. These synchronized etalons could be used for standardizing the wavelengths of transmitter lasers in large-scale WDM wavelength division multiplexed networks     

Cooperative beamforming in cognitive radio systems without feedback of receiver beamforming vectors to transmitter

Wireless Networks - In this paper, we investigate the problem of transceiver beamforming and power allocation in the downlink of a multiple input multiple output Cognitive radio system. In this...     

Microwave photonic direct-sequence transmitter and heterodyne correlation receiver

This paper proposes and demonstrates a new architecture for the transmission, heterodyne reception, and correlation of direct-sequence (DS) signals encoded onto an optical carrier. The approach is practical for pseudo-noise in-modulated laser radar and free-space optical-code-division multiple-access communications. Although the local oscillator is free running, we show that the received signal is free from laser phase noise. Furthermore, by applying DS coding to both the transmitted signal and the local oscillator, the delay required for correlation can be realized via a combination of electrical and optical means.