Comparisons of Short-Prefix Based Channel Estimation in Single-Carrier Communication Systems

In this paper, we compare the performance between channel estimation based on compressed sensing (CS) and time-domain least square (LS) for single-carrier (SC) communication system. Unlike the conventional channel estimation techniques such as frequency domain LS which is used in the condition that the length of pilot sequence is equal to data sequence, the estimation scheme based on CS requires smaller length of pilot sequence. In this paper, the corresponding system structure is presented. Zadoff-Chu sequence is used to generate the pilot sequence, which is shown to perform better in forming measurement matrix of CS than pseudo random sequence. Simulation results demonstrate that channel estimation based on CS achieves a better bit error rate (BER) performance than time domain LS with a smaller pilot sequence and thus raising data rate of the SC communication system.

Fast frequency-domain equalization for single-carrier V-BLAST systems over multipath channel

A low complex minimum mean-square error frequency-domain decision feedback （MMSE-FDDF） equalization algorithm is proposed in this paper for the single-carrier V-BLAST systems. Exploiting the factor that the discrete Fourier transform （DFT） is unitary, the proposed receiver can equalize the signals by the MMSE detecting to the spectrums in the frequency domain instead of the waveforms in the time domain. In order to obtain the right decisions, the detector must be able to equalize the overall spectrum with regard to each layer. This work can be performed very efficiently since the system matrix has been designed as a special block-circulant-block matrix. Similar to other V-BLAST-like systems, the detecting order has strong impact on the performance of MMSE-FDDF. Therefore, we further give a fast optimally sorting scheme for the MMSE-FDDF architecture. By using the newly constructed matrix, the coefficients computation and the sorting can be combined into one process, and then we employ the modified Gram-Schmidt （MGS） to simplify the process. The simulation results and the computational complexity analysis show that the proposed MMSE-FDDF has better tradeoff between the performance and the complexity than the existing algorithms. In addition, MMSE-FDDF can avoid the performance floor caused by the overlap-and-save technique in the severe dispersive channel.

LLR calculation for LDPC coded SCBT in 60 GHz WPAN

The single-carrier block transmission（SCBT）,a.k.a.,single-carrier frequency-domain equalization（SC-FDE）,is being considered as an option technique for the wireless personal area network（WPAN） operating at 60 GHz.It is found that for residential environment,in non-line-of-sight（NLOS） multi-path channels,the SCBT is much more effective to combat the inter-symbol interference（ISI） compared with orthogonal frequency division multiplexing（OFDM）.Low-density parity-check（LDPC） codes are a class of linear block codes which provide near capacity performance on a large collection of data transmission and storage channels while simultaneously admitting implementable decoders.To facilitate using LDPC codes for SCBT system,a new log-likelihood ratio（LLR） calculation method is proposed based on pilot symbols（PS）.Golay Sequences whose sum autocorrelation has a unique peak and zero sidelobe are used for creating the PS.The position and length of the PS are not fixed in the data blocks.The simulation results show that the proposed method can significantly improve the LDPC decoding performance in SCBT system.This is very promising to support ultra high-data-rate wireless transmission.

Spatial Load Balancing in Wide-Area Wireless Networks

Load balancing is typically used in the frequency domain of cellular wireless networks to balance paging, access, and traffic load across the available bandwidth. In this paper, we extend load balancing into the spatial domain, and we develop two approaches--network load balancing and single-carrier multilink--for spatial load balancing. Although these techniques are mostly applied to cellular wireless networks and Wi-Fi networks, we show how they can be applied to EV-DO, a 3G cellular data network. When a device has more than one candidate server, these techniques can be used to determine the quality of the channel between a server and the device and to determine the Ipad on each server. The proposed techniques leverage the advantages of existing EV-DO network architecture and are fully backward compatible. Network operators can substantially increase network capacity and improve user experience by using these techniques. Combining load balancing in the frequency and spatial domains improves connectivity within a network and allows resources to be optimally allocated according to the p-fair criterion. Combined load balancing further improves performance.

A RF receiver frontend for SC-UWB in a 0.18-μm CMOS process

A radio frequency （RF） receiver frontend for single-carrier ultra-wideband （SC-UWB） is presented. The front end employs direct-conversion architecture, and consists of a differential low noise amplifier （LNA）, a quadrature mixer, and two intermediate frequency （IF） amplifiers. The proposed LNA employs source inductively degenerated topology. First, the expression of input impedance matching bandwidth in terms of gate-source ca- pacitance, resonant frequency and target Sll is given. Then, a noise figure optimization strategy under gain and power constraints is proposed, with consideration of the integrated gate inductor, the bond-wire inductance, and its variation. The LNA utilizes two stages with different resonant frequencies to acquire flat gain over the 7.1-8.1 GHz frequency band, and has two gain modes to obtain a higher receiver dynamic range. The mixer uses a double bal- anced Gilbert structure. The front end is fabricated in a TSMC 0.18-μm RF CMOS process and occupies an area of 1.43 mm2. In high and low gain modes, the measured maximum conversion gain are 42 dB and 22 dB, input 1 dB compression points are -40 dBm and -20 dBm, and Sll is better than -18 dB and -14.5 dB. The 3 dB IF bandwidth is more than 500 MHz. The double sideband noise figure is 4.7 dB in high gain mode. The total power consumption is 65 mW from a 1.8 V supply.

Dimming control scheme based on hybrid LACO-SCFDM for visible light communications

This paper proposes a hybrid layered asymmetrically clipped optical(HLACO) single-carrier frequency-division multiplexing(SCFDM) scheme for dimmable visible light communication. It designs a signal structure that combines layered asymmetrically clipped optical(LACO)-SCFDM and negative LACO-SCFDM in proportion for improving the inherent weaknesses of orthogonal frequency-division multiplexing(OFDM)-based dimmable schemes and further enhancing the system performance. Compared to the HLACO-OFDM-based dimming scheme, it obtains a lower bit error ratio and enables efficient communication over broader dimming range. Its spectral efficiency realizes 2.875 bit·s^(-1)·Hz^(-1) within the dimming range of 30%–70%, and the attainable average spectral efficiency gains exceed at least 19.21% compared to other traditional dimmable schemes.

Beam squint effect on high-throughput millimeter-wave communication with an ultra-massive phased array

An ultra-massive phased array can be deployed in high-throughput millimeter-wave(mmWave)communication systems to increase the transmission distance.However,when the signal bandwidth is large,the antenna array response changes with the frequency,causing beam squint.In this paper,we investigate the beam squint effect on a high-throughput mmWave communication system with the single-carrier frequency-domain equalization transmission scheme.Specifically,we first view analog beamforming and the physical channel as a spatial equivalent channel.The characteristics of the spatial equivalent channel are analyzed which behaves like frequency-selective fading.To eliminate the deep fading points in the spatial equivalent channel,an advanced analog beamforming method is proposed based on the Zadoff-Chu(ZC)sequence.Then,the low-complexity linear zero-forcing and minimum mean squared error equalizers are considered at the receiver.Simulation results indicate that the proposed ZC-based analog beamforming method can effectively mitigate the performance loss by the beam squint.