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.     

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。     

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.     

Nyquist's problem—The joint optimization of transmitter and receiver in pulse amplitude modulation

Using a criterion of minimum mean square interference, the optimum, linear, generally unrealizable receiver for a noisy pulse amplitude modulation (PAM) system is specified for the case in which a finite number of identically shaped pulses with random, possibly correlated amplitudes are transmitted. The interference is composed of both noise and intersymbol interference. The optimum receiver, using the same criterion, is also obtained for the case in which the intersymbol interference is constrained to be zero. The average error probabilities associated with these receivers are compared with each other and with a matched filter receiver in one example. In addition, formulas for optimum transmitted pulse shapes are derived, and the joint optimization of transmitter and receiver is carried out in detail for the case of signaling through a noisy RC filter. Other formulas enable one to explore the dependence of the minimum mean square interference on the data rate, the noise spectrum, the impulse response of the transmission medium, and the autocorrelation of the message sequence.     

基于混合精度ADC量化的大规模MIMO系统能效联合优化算法

针对在接收端采用混合精度的数模转换器（analog-to-digitalconverter,ADC）的大规模MIMO系统上行链路,提出一种能效优化算法。在采用最大比合并（maximumratiocombining,MRC）检测算法的基础上,推导得到系统上行链路能效的近似闭式表达式。首先确定高精度ADC的占比率,再以低分辨率ADC的量化精度、用户的发射功率和基站端天线数为优化目标的3个变量进行交替迭代得出最优的能效值;并进一步通过调整高精度ADC的占比率分析其对能效和频效的影响。仿真结果表明,所提算法具有较高的能效值,并且可以通过调整占比率实现能效与频效更好地折中。     

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.     

Robust joint optimization for MIMO AF multiple-relay systems with correlated channel uncertainties

In the paper, robust joint optimization of the source/relays precoders and destination equalizer is proposed for non-regenerative dual-hop multiple-input multiple-output (MIMO) amplify-and-forward (AF) multiple-relay systems with correlated channel uncertainties. By taking the imperfect channel state information (CSI) into consideration, the robust transceiver/relays joint optimization is developed based on the minimum mean-squared error (MMSE) criterion under individual power constraints at the source and relays. The optimization problem of precoding and amplifying matrices under power constraints belongs to neither concave nor convex so that a nonlinear matrix-form conjugate gradient (MCG) algorithm is applied to explore local optimal solutions. Simulation results illustrate that the robust transceiver/relays joint architecture for an AF-MIMO multiple-relay system outperforms the non-robust transceiver/relays design.     

Simplified transmitter design for MIMO systems with channel uncertainty

This article investigates transmitter design in Rayleigh fading multiple input multiple output (MIMO) channels with spatial correlation when there are channel uncertainties caused by a combined effect of channel estimation error and limited feedback. To overcome the high computational complexity of the optimal transmit power allocation, a simple and suboptimal allocation is proposed by exploiting the transmission constraint and differentiating a bound based on Jensen inequality on the channel capacity. The simulation results show that the mutual information corresponding to the proposed power allocation closely approaches the channel capacity corresponding to the optimal one and meanwhile the computational complexity is greatly reduced.     

大规模MIMO系统中基于能效最大化的资源联合优化算法

针对信道条件未知的多小区大规模多输入多输出（MIMO）系统,提出一种对导频序列长度、导频符号功率以及数据符号功率进行联合优化的资源分配算法。采用最大比合并（MRC）接收,考虑电功率和导频污染的影响,并对最大传输功率进行约束从而建立起以能效（EE）最大化为目标的非凸函数模型。根据分数规划的性质,首先将分数形式转化成减式形式,进而分解成一系列凸函数之差（DC）的问题,最后采用交替优化算法联合调整 3 个变量从而达到能效最大化的目标。仿真结果表明,随着最大符号传输功率的增加,所提方案仍然能保持良好系统能效性能。     

On optimum transmission power strategy in MIMO systems with covariance feedback

We study the optimum transmission power strategy in a multiple-input multiple-output (MIMO) system with perfect channel state information (CSI) at the receiver and channel covariance matrix at the transmitter. A necessary and sufficient condition is derived for the optimum power allocation at the transmitter to maximize the average mutual information. Furthermore, we apply this result to extend the discussion on optimality of beamforming to general cases of transmitting in m directions for achieving capacity.     

Blind adaptive receiver for uplink multiuser massive MIMO systems

Herein, we consider uplink multiuser massive multiple‐input multiple‐output systems when multiple users transmit information symbols to a base station (BS) by applying simple space‐time block coding (STBC). At the BS receiver, two detection filters for each user are used to detect the STBC information symbols. One of these filters is for odd‐indexed symbols and the other for even‐indexed symbols. Using constrained output variance metric minimization, we first derive a special relation between the closed‐form optimal solutions for the two detection filters. Then, using the derived special relation, we propose a new blind adaptive algorithm for implementing the minimum output variance‐based optimal filters. In the proposed adaptive algorithm, filter weight vectors are updated only in the region satisfying the special relation. Through a theoretical analysis of the convergence speed and a computer simulation, we demonstrate that the proposed scheme exhibits faster convergence speed and lower steady‐state bit error rate than the conventional scheme.     

Transceiver optimization for multiuser MIMO systems

We consider the uplink of a multiuser system where the transmitters as well as the receiver are equipped with multiple antennas. Each user multiplexes its symbols by a linear precoder through its transmit antennas. We work with the system-wide mean squared error as the performance measure and propose algorithms to find the jointly optimum linear precoders at each transmitter and linear decoders at the receiver. We first work with the case where the number of symbols to be transmitted by each user is given. We then investigate how the symbol rate should be chosen for each user with optimum transmitters and receivers. The convergence analysis of the algorithms is given, and numerical evidence that supports the analysis is presented.     

On transmitter gain/phase imbalance compensation at receiver

This letter explores the benefits of compensating for transmitter gain and phase imbalances in a receiver for quadrature communication systems. It is assumed that the gain and phase imbalances are introduced at the transmitter only. The Gram-Schmidt orthogonalization procedure is used at the receiver to compensate for the imbalances. Computer simulation has been performed to study a coherent differential QPSK communication system. It has been found that the bit error rate performance is improved significantly if the transmitter phase imbalance is compensated for. However, no improvement can be obtained if the transmitter gain imbalance is compensated for     

Linear transmitter precoding design for downlink of multiuser MIMO systems

Presented is the design of a set of linear transmitter precoding vectors for the downlink of a multiuser MIMO system, using the maximum signal-to-jamming and noise ratio for each user criterion, subject to a transmit power constraint. The proposed scheme does not impose any restrictions on the number of transmit antennas as do many conventional methods. Simulation results have shown the superiority of the proposed scheme compared to the conventional transmitter precoding schemes.     

Transmitter and receiver optimization in multicarrier CDMA systems

We consider transmitter and receiver optimization in multicarrier code-division multiple-access (MC-CDMA) systems under Rayleigh fading channels. Receiver optimization is performed in a decentralized manner, while transmitter optimization can be performed through either centralized or decentralized control of the powers of different carriers. Results show that when the number of users is smaller than or equal to the number of carriers, each transmitter often tends to concentrate its power on a different carrier which does not suffer deep fading. The MC-CDMA system then tends to a frequency-division multiple-access system with near-optimal frequency assignment. When the number of users gets large, each user tends to choose more than one carrier, which do not suffer deep fading, while interference suppression is performed across the chosen carriers by the corresponding receiver     

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.     

A 0.18-/spl mu/m SiGe BiCMOS receiver and transmitter chipset for SONET OC-768 transmission systems

A 43-Gb/s receiver (Rx) and transmitter (Tx) chip set for SONET OC-768 transmission systems is reported. Both ICs are implemented in a 0.18-/spl mu/m SiGe BiCMOS technology featuring 120-GHz f/sub T/ and 100 GHz f/sub max/. The Rx includes a limiting amplifier, a half-rate clock and data recovery unit, a 1:4 demultiplexer, a frequency acquisition aid, and a frequency lock detector. Input sensitivity for a bit-error rate less than 10/sup -9/ is 40 mV and jitter generation better than 230 fs rms. The IC dissipates 2.4 W from a -3.6-V supply voltage. The Tx integrates a half-rate clock multiplier unit with a 4:1 multiplexer. Measured clock jitter generation is better than 170 fs rms. The IC consumes 2.3 W from a -3.6-V supply voltage.     

Compressive image broadcasting in MIMO systems with receiver antenna heterogeneity

In this work we consider image delivery in MIMO broadcast networks with diverse channel quality and varying numbers of antennas across receivers. In such systems, performance is normally constrained by the weakest users with either a low channel SNR or only a single receive antenna. To address both dimensions of heterogeneity, we propose a new analog image delivery system that adapts seamlessly along both dimensions simultaneously. Our sender scales the DWT coefficients according to a power allocation strategy, and generates linear combinations of the coefficients using compressive sensing (CS), before transmitting them with amplitude modulation. On the receiving side, the received physical layer symbols are passed directly to the source decoder without conventional MIMO decoding, and the DWT coefficients are recovered using a CS decoder.There are two main contributions of our system. First, integrating CS into MIMO transmission ensures that the reconstructed image quality at the receivers is commensurate with both the channel SNR and the MIMO channel dimension. Second, we introduce a power allocation strategy to achieve a performance tradeoff between receivers with different antenna numbers. Experimental results show that the proposed system outperforms both the analog reference SoftCast and the conventional digital system known as HM-STBC. The average gain is 2.92 dB over SoftCast for single-antenna users and 1.53 dB over HM-STBC for two-antenna users.