Huarui Yin

Monobit digital receivers: design, performance, and application to impulse radio

Digital receivers for future high-rate high-bandwidth communication systems will require large sampling rate. This is especially true for ultra-wideband (UWB) communications with impulse radio (IR) modulation. Due to high complexity and large power consumption, multibit high-rate analog-to-digital converter (ADC) is difficult to implement. Monobit receiver has been previously proposed to relax the need for high-rate ADC. In this paper, we derive optimal digital processing architecture for receivers based on monobit ADC with a certain over-sampling rate and the corresponding theoretically achievable performance. A practically appealing suboptimal iterative receiver is also proposed. Iterative decision-directed weight estimation, and small sample removal are distinctive features of the proposed detector. Numerical simulations show that compared with full resolution matched filter based receiver, the proposed low complexity monobit receiver incurs only 2 dB signal to noise ratio (SNR) loss in additive white Gaussian noise (AWGN) and 3.5dB SNR loss in standard UWB fading channels.

Degrees of Freedom Region for an Interference Network With General Message Demands

We consider a single-hop interference network with K transmitters and J receivers, all having M antennas. Each transmitter emits an independent message and each receiver requests an arbitrary subset of the messages. This generalizes the well-known K -user M-antenna interference channel, where each message is requested by a unique receiver. For our setup, we derive the degrees of freedom (DoF) region. The achievability scheme generalizes the interference alignment schemes proposed by Cadambe and Jafar. In particular, we achieve general points in the DoF region by using multiple base vectors and aligning all interferers at a given receiver to the interferer with the largest DoF. As a byproduct, we obtain the DoF region for the original interference channel. We also discuss extensions of our approach where the same region can be achieved by considering a reduced set of interference alignment constraints, thus reducing the time-expansion duration needed. The DoF region for the considered system depends only on a subset of receivers whose demands meet certain characteristics. The geometric shape of the DoF region is also discussed.

Finite-resolution digital receiver design for impulse radio ultra-wideband communication

Receiver design for impulse radio based ultrawideband (UWB) communication is a challenge. High sampling rate high resolution digital receiver is usually difficult to implement. Some tradeoffs can be made on the digital receiver, such as limiting amplitude resolution to only one bit, which results in a previously considered monobit receiver. In this paper, we consider the design of finite-resolution digital UWB receivers. We derive the optimal post-quantization processing, and analyze the achievable bit-error rate performance using an approximation of the log-likelihood ratio. Optimal thresholds for 4- and 3-level quantization are obtained. Training-based receiver template estimation is presented. Our work discloses the incremental gain that additional quantization levels offer and the results provide useful guidelines for designing impulse radio UWB digital receivers.

Drone-assisted public safety wireless broadband network

A nationwide interoperable public safety wireless broadband network is being planned by the First Responder Network Authority (FirstNet) under the auspices of the United States government. The public safety network shall provide the needed wireless coverage in the wake of an incident or a disaster. This paper proposes a drone-assisted multi-hop device-to-device (D2D) communication scheme as a means to extend the network coverage over regions where it is difficult to deploy a landbased relay. The resource are shared using either time division or frequency division scheme. Efficient algorithms are developed to compute the optimal position of the drone for maximizing the data rate, which are shown to be highly effective via simulations.

The structure and performance on an orthogonal sinusoidal correlation receiver of impulse radio

Impulse radio (IR) is a competitive candidate for ultra-wide bandwidth (UWB) systems. A key feature of time-hopping IR is the subnanosecond pulses used to convey information. Analysis of such time-hopping schemes has been reported under a variety of assumptions. The performance of such IR systems is very sensitive to timing error, at least in part due to the very narrow pulses. A new structure of an orthogonal sinusoidal correlation receiver (OSCR) in IR systems is proposed to receive the subnanosecond pulses. Its tolerance to timing error is investigated. The receiver is proved to be efficient, practical and robust.

Degrees of freedom region for an interference network with general message demands

We consider a single-hop interference network with K transmitters and J receivers, all having M antennas. Each transmitter emits an independent message and each receiver requests an arbitrary subset of the messages. This generalizes the well-known K -user M-antenna interference channel, where each message is requested by a unique receiver. For our setup, we derive the degrees of freedom (DoF) region. The achievability scheme generalizes the interference alignment schemes proposed by Cadambe and Jafar. In particular, we achieve general points in the DoF region by using multiple base vectors and aligning all interferers at a given receiver to the interferer with the largest DoF. As a byproduct, we obtain the DoF region for the original interference channel. We also discuss extensions of our approach where the same region can be achieved by considering a reduced set of interference alignment constraints, thus reducing the time-expansion duration needed. The DoF region for the considered system depends only on a subset of receivers whose demands meet certain characteristics. The geometric shape of the DoF region is also discussed.

Selective relaying schemes for distributed space-time coded regenerative relay networks

In distributed space-time (DST)-coded regenerative relay networks, demodulation error produced by relays degrades the receiver performance significantly. To mitigate this disadvantage, two threshold-based selective relaying schemes are proposed, that is, centralised selecting scheme and distributed selecting scheme, where each relay forwards signals only if its received signal-noise ratio is larger than a threshold. Both proposed schemes can work well with arbitrary modulation constellation and any number of relays and no matter whether the source-destination channel is available or not. Simulation results show both proposed selective relaying schemes outperform conventional schemes significantly and the improvement increases as the scale of relay network grows. Centralised selecting has a slightly better performance than the distributed selecting. However, the latter has a far lower system cost. This contribution provides two useful relaying mechanisms to mitigate error propagation.

Pilot sequences allocation in TDD massive MIMO systems

Massive multiple-input multiple-output (MIMO) has been proposed as a key technology for the future fifth generation (5G) cellular networks. In time division duplex (TDD) massive MIMO systems, pilot contamination caused by channel estimation error is crucial to the system performance. In this paper, we propose a pilot sequences allocation strategy to mitigate the pilot contamination. In this strategy, the pilot sequences sets are identical for center users, but mutually orthogonal for edge users in different cells. With mitigated pilot contamination, we analytically determine the approximate system capacity which is accurate when the number of antennas at the base station tends to infinite. The simulation results show that the proposed pilot sequences allocation strategy achieves higher system capacity than the traditional pilot sequences allocation strategy whose sequences reuse rate is one or three. There also exists an optimal number of pilot sequences in different SNR to maximize the system capacity.

Low Complexity Tri-Level Sampling Receiver Design for UWB Time-of-Arrival Estimation

In this paper, the effect of finite-level quantization on UWB time-of-arrival (TOA) estimation is investigated. The scheme of optimized quantization threshold combined with the post-quantization processing is derived, which is shown to provide satisfactory gains in the system performance. The TOA estimation errors of several low-resolution sampling approaches are compared via Monte Carlo simulation, where the tri-level quantizer is of particular interest due to its simplicity and capability. We demonstrate that the tri-level sampling receiver, with use of the proposed scheme provides an outstanding performance in TOA estimation with an affordable cost and low complexity.

Monobit Digital Receivers for QPSK: Design, Performance and Impact of IQ Imbalances

Future communication system requires large bandwidths to achieve high data rates, thus rendering analog-to-digital conversion (ADC) a bottleneck due to its high power consumption. In this paper, we consider monobit receivers for QPSK. The optimal monobit receiver under Nyquist sampling is obtained and its performance is analyzed. Then, a suboptimal but low-complexity receiver is proposed. The effect of imbalances between In-phase (I) and Quadrature (Q) branches is carefully examined. To combat the performance loss due to IQ imbalances, monobit receivers based on double training sequences and eight-sector phase quantization are proposed. Numerical simulations show that the low-complexity suboptimal receiver suffers 3dB signal-to-noise-ratio (SNR) loss in additive white Gaussian noise (AWGN) channels and only 1dB SNR loss in multipath channels compared with matched-filter monobit receiver with perfect channel state information (CSI). It is further demonstrated that the amplitude imbalance has essentially no effect on monobit receivers. In AWGN channels, receivers based on double training sequences can efficiently compensate for the SNR loss without complexity increase, while receivers with eight-sector phase quantization can almost completely eliminate the SNR loss caused by IQ imbalances. In dense multipath channels, the effect of imbalances on monobit receivers is slight.