Bit Error Rate Constraint Research Articles

Threshold-Based Substream Selection for Closed-Loop Spatial Multiplexing

We propose a low-complexity closed-loop spatial multiplexing method with limited feedback over multi-input-multi-output (MIMO) fading channels. The transmit adaptation is simply performed by selecting transmit antennas (or substreams) by comparing their signal-to-noise ratios to a given threshold with a fixed nonadaptive constellation and fixed transmit power per substream. We analyze the performance of the proposed system by deriving closed-form expressions for spectral efficiency, average transmit power, and bit error rate (BER). Depending on practical system design constraints, the threshold is chosen to maximize the spectral efficiency (or minimize the average BER) subject to average transmit power and average BER (or spectral efficiency) constraints, respectively. We present numerical and Monte Carlo simulation results that validate our analysis. Compared to open-loop spatial multiplexing and other approaches that select the best antenna subset in spatial multiplexing, the numerical results illustrate that the proposed technique obtains significant power gains for the same BER and spectral efficiency. We also provide numerical results that show improvement over rate-adaptive orthogonal space-time block coding, which requires highly complex constellation adaptation. We analyze the impact of feedback delay using analytical and Monte Carlo approaches. The proposed approach is arguably the simplest possible adaptive spatial multiplexing system from an implementation point of view. However, our approach and analysis can be extended to other systems using multiple constellations and power levels.

Joint Power Minimization in Wireless Relay Channels

Energy-constrained multihop wireless links are considered, where the total power consumption is minimized under given requirements on the end-to-end bit error rate (BER). As multihop transmissions are known to be able to save transmission energy in a wireless environment, we study the optimal power scheduling schemes over intermediate hops when the source- relays-destination link can be modeled as cascaded binary symmetric channels. The problem is formulated with an end- to-end BER constraint, and the resulting power consumption is compared with that of the individual link requirement strategy where each hop assigns power under a per-link BER constraint. Results show that the proposed joint power scheduling strategy can achieve a maximum power reduction factor of M in an M-hop route.

How Accurate does Channel Prediction Need to be in Adaptive V-BLAST Systems?

Since the accuracy of channel prediction influences the performance of adaptive multiple-input-multiple-output (MIMO) systems in Rayleigh fading channels, we analyze the performance of adaptive V-BLAST systems with a minimum-mean-square-error (MMSE) channel predictor in this paper. Considering the channel prediction error, we obtain the closed-form expressions for the bit-error-rate (BER) and throughput of adaptive V-BLAST systems, and maximize system transmission rate by choosing optimum block length under BER constraint. The numerical results reveal the critical value of channel prediction error below which systems can match the transmission rate of the systems with perfect channel prediction.

Efficient synthesis methodology for optimal inverter-based transimpedance amplifiers

In this paper, we present a new synthesis methodology that facilitates the design automation of maximum bandwidth transimpedance amplifier (TIA) for optical communications under the constraint of a specific bit error rate. Our synthesis methodology is based on newly developed models that characterize the input referred noise and bandwidth. Our technique provides the optimal parameters of the transimpedance amplifier for maximizing the bandwidth. These optimal parameters are mapped to equivalent circuit parameters to achieve the optimal sizing of the TIA. Our methodology is characterized by its very fast design convergence as well as better results compared to conventional design techniques. We applied our synthesis methodology in designing a TIA for optical interconnect systems using the 0.25?m and 0.18?m CMOS technologies.

Spatial scheduling in multiuser wireless systems: from power allocation to admission control

Given a zero forcing transmit beamforming, we focus on how the multi-antenna access point distributes the scarce resource (power) among the single-antenna terminals. Since there is a clear trade-off between the satisfaction of the individual needs and the global performance of the cell, several criteria are proposed, ranging from a classical physical layer point of view of capacity (rate) maximization to bit error rate (BER)-based cost functions, which are closer to the second layer of the protocol stack. Between two traditional techniques, namely the uniform power allocation and the equal BER and rate, a new one is proposed, which ultimately provides an intermediate performance. Then, we add BER (or signal to noise ratio) constraints so that the admission control problem has to be solved. Among traditional options, we propose a new mechanism to balance the above-mentioned trade-off between the total performance and the particular user behavior. The results in terms of fairness are presented by a mean vs. variance plot and by the Gini plot

Multirate zero-forcing Tx-Rx design for MIMO channel under BER constraints

This paper is concerned with communicating parallel independent streams of data, possibly of different rates, through a multiple-input multiple-output channel. Each data stream is required to satisfy a bit-error-rate (BER) constraint. This scenario arises in multimedia communications. We find the linear zero-forcing transmitter-receiver (Tx-Rx) matrix pair that requires the minimum transmitter power to achieve the BER constraints. It is well known that the Tx-Rx pair can be chosen to partition the matrix channel into scalar subchannels corresponding to singular values, and different data streams can be transmitted through different subchannels. This design is suboptimum in general. The optimum design has the following structure. The set of input data streams is partitioned into groups called signal groups. The set of subchannels is conformably partitioned into subchannel groups. Each signal group is collectively transmitted through its assigned subchannel group. With each signal/subchannel group pair is associated a unitary matrix that mixes the signals at the transmitter and unmixes them at the receiver. We derive a simple algorithm to determine the optimum signal and subchannel groups. We then use a known algorithm from majorization theory to determine the unitary matrices. Using these, we completely specify the optimum Tx-Rx pair.

Adaptive Coded Modulation With Receive Antenna Diversity and Imperfect Channel Knowledge at Receiver and Transmitter

Unifying and generalizing the works of Cai and Giannakis and Oien et al., the performance of an adaptive trellis-coded modulation system where receive antenna diversity is implemented by means of maximum ratio combining is analyzed and optimized. As in the work of Cai and Giannakis, the analysis is done in the presence of both estimation and prediction errors. Rayleigh fading on each subchannel is considered, with the estimation and prediction being performed independently on each subchannel. The system optimization process is done in such a way that the throughput is maximized under a bit-error-rate (BER) constraint. The numerical example employs a Jakes-fading spectrum and shows how the power should be distributed between pilot and data symbols and how often pilot symbols should be transmitted for maximum throughput under an instantaneous (with respect to the predicted channel) BER constraint.

Optimized nonuniform PSK for multiclass traffic and its application to space-time block codes

We construct nonuniform phase-shift keying (PSK) constellations that provide unequal error protection for multiclass traffic such as compressed voice and video data. Then closed-form expressions expression for the exact bit-error rate (BER) of the nonuniform PSK constellations is derived in multiple receive-antenna systems over Rayleigh fading channels. Based on this BER analysis, we optimize the nonuniform PSK constellations such that the BERs of all the bits of each class are equalized or such that the total transmission power is minimized subject to the average BER constraints. In particular, we demonstrate that even for transmitting single-class traffic, the optimized nonuniform PSK constellations can be better than the conventional uniform PSK. Finally, we extend the nonuniform PSK constellations to space-time coded communications systems with multiple transmit and multiple receive antennas.

Effects of time delay spread on constant-power constant-symbol-rate adaptive QAM

Average throughput and bit error rate (BER) are derived for constant-power adaptive quadrature amplitude modulation over frequency selective fading channels corrupted by ISI and Gaussian noise. Effects of time delay spread on average throughput are studied under different BER constraints. Results show that useful performance can be achieved without diversity or equalisation.

Adaptive Modulation Systems for Predicted Wireless Channels

When adaptive modulation is used to counter short-term fading in mobile radio channels, signaling delays create problems with outdated channel state information. The use of channel power prediction will improve the performance of the link adaptation. It is then of interest to take the quality of these predictions into account explicitly when designing an adaptive modulation scheme. We study the optimum design of an adaptive modulation scheme based on uncoded M-quadrature amplitude modulation, assisted by channel prediction for the flat Rayleigh fading channel. The data rate, and in some variants the transmit power, are adapted to maximize the spectral efficiency, subject to average power and bit-error rate constraints. The key issues studied here are how a known prediction error variance will affect the optimized transmission properties, such as the signal-to-noise ratio (SNR) boundaries that determine when to apply different modulation rates, and to what extent it affects the spectral efficiency. This investigation is performed by analytical optimization of the link adaptation, using the statistical properties of a particular, but efficient, channel power predictor. Optimum solutions for the rate and transmit power are derived, based on the predicted SNR and the prediction error variance.

Efficient signaling schemes for wideband space-time wireless channels using channel state information

An orthogonal decomposition of a general wideband space-time frequency selective channel is derived assuming antenna arrays at both the transmitter and receiver. Knowledge of channel state information is assumed at both the transmitter and receiver. The decomposition provides a framework for efficiently managing the degrees of freedom in the space-time channel to optimize any combination of bit-error rate and throughput in single-user or multiuser applications. The decomposition is used to derive efficient signaling schemes and receiver structures for a variety of scenarios. For a fixed throughput system, we investigate a power allocation scheme that minimizes the effective bit-error rate. In addition, a strategy to maximize the throughput under a worst-case bit-error rate constraint is proposed. For multiuser applications, we propose a signaling scheme that achieves orthogonality among users by exploiting the temporal channel modes which are common to all users. The effect of imperfect channel state information at the transmitter is also investigated.

Effects of multipath diversity on adaptive QAM in frequency selective Rayleigh fading channels

We derive the average bit error rate (BER) and the average throughput for adaptive quadrature amplitude modulation (AQAM) with constant transmit power over frequency selective Rayleigh fading channels. Based on these derived BER and throughput expressions, we go on to investigate the effect of multipath diversity on AQAM using two BER constraints.