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25 December 2011, Volume 9 Issue 4

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The whole issue of ZTE Communications December 2011, Vol. 9 No. 4

2011, 9(4):  0. 

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Special Topic

Guest Editorial: Advances in Digital Front-End and Software RF Processing: Part I

Jun Fang, Fa-Long Luo, Mikko Valkama, Serioja Ovidiu Tatu and Tomohisa Wada

2011, 9(4):  1-2. 

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Polyphase Filter Banks for Embedded Sample Rate Changes in Digital Radio Front-Ends

Mehmood Awan, Yannick Le Moullec, Peter Koch, and Fred Harris

2011, 9(4):  3-9. 

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This paper presents efficient processing engines for software-defined radio (SDR) front-ends. These engines, based on a polyphase channelizer, perform arbitrary sample-rate changes, frequency selection, and bandwidth control. This paper presents an M-path polyphase filter bank based on a modified N-path polyphase filter. Such a system allows resampling by arbitrary ratios while performing baseband aliasing from center frequencies at Nyquist zones that are not multiples of the output sample rate. This resampling technique is based on sliding cyclic data load interacting with cyclic-shifted coefficients. A non-maximally-decimated polyphase filter bank (where the number of data loads is not equal to the number of M subfilters) processes M subfilters in a time period that is less than or greater than the M data loads. A polyphase filter bank with five different resampling modes is used as a case study for embedded resampling in SDR front-ends. These modes are (i) maximally decimated, (ii) under-decimated, (iii) over-decimated, and combined up- and down-sampling with (iv) single stride length, and (v) multiple stride lengths. These modes can be used to obtain any required rational sampling rate change in an SDR front-end based on a polyphase channelizer. They can also be used for translation to and from arbitrary center frequencies that are unrelated to the output sample rates.

Design of Software-Defined Down-Conversion and Up-Conversion: An Overview

Yue Zhang, Li-Ke Huang, Carsten Maple, and Qing Xuan

2011, 9(4):  10-14. 

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In recent years, much attention has been paid to software-defined radio (SDR) technologies for multimode wireless systems. SDR can be defined as a radio communication system that uses software to modulate and demodulate radio signals. This article describes concepts, theory, and design principles for SDR down-conversion and up-conversion. Design issues in SDR down-conversion are discussed, and two different architectures, super-heterodyne and direct-conversion, are proposed. Design issues in SDR up-conversion are also discussed, and trade-offs in the design of filters, mixers, NCO, DAC, and signal processing are highlighted.

Practical Non-Uniform Channelization for Multistandard Base Stations

Álvaro Palomo Navarro, Rudi Villing, and Ronan J. Farrell

2011, 9(4):  15-24. 

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A Multistandard software-defined radio base station must perform non-uniform channelization of multiplexed frequency bands. Non-uniform channelization accounts for a significant portion of the digital signal processing workload in the base station receiver and can be difficult to realize in a physical implementation. In non-uniform channelization methods based on generalized DFT filter banks, large prototype filter orders are a significant issue for implementation. In this paper, a multistage filter design is applied to two different non-uniform generalized DFT-based channelizers in order to reduce their filter orders. To evaluate the approach, a TETRA and TEDS base station is used. Experimental results show that the new multistage design reduces both the number of coefficients and operations and leads to a more feasible design and practical physical implementation.

Crest Factor Reduction for OFDM Using Selective Subcarrier Degradation

R. Neil Braithwaite

2011, 9(4):  25-31. 

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This paper describes a crest factor reduction (CFR) method that reduces peaks in the time domain by modifying selected data subcarriers within an OFDM signal. The data subcarriers selected for modification vary with each symbol interval and are limited to those subcarriers whose data elements are mapped onto the outer boundary of the constellation. In the proposed method, a set of peaks are identified within an OFDM symbol interval. Data subcarriers whose data element has a positive or negative correlation with the set peak are selected. For a subcarrier with an outer element and a significant positive correlation, a bit error (reversal) is intentionally introduced. This moves the data element to the opposite side of the constellation. Outer elements on negatively-correlated subcarriers are increased in magnitude along the real or imaginary axis. Experimental results show that selecting the correct subcarriers for bit reversals and outward enhancements reduces the peak-to-average power ratio (PAPR) of the OFDM signal to a target value and limits in-band degradation measured by bit error rate (BER) and error vector magnitude (EVM).

An Antenna Diversity Scheme for Digital Front-End with OFDM Technology

Fa-Long Luo, Ward Williams, and Bruce Gladstone

2011, 9(4):  32-34. 

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In this paper, we propose a new antenna diversity scheme for OFDM-based wireless communication and digital broadcasting applications. Compared with existing schemes, such as post-fast Fourier transform (FFT), pre-FFT, and polyphase-based filter-bank, the proposed scheme performs optimally and has very low computational complexity. It offers a better compromise between performance, power consumption, and complexity in real-time implementation of the receivers of broadband communication and digital broadcasting systems.

A Histogram-Based Static-Error Correction Technique for Flash ADCs

Armin Jalili, J Jacob Wikner, Sayed Masoud Sayedi, and Rasoul Dehghani

2011, 9(4):  35-41. 

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High-speed, high-accuracy data converters are attractive for use in most RF applications. Such converters allow direct conversion to occur between the digital baseband and the antenna. However, high speed and high accuracy make the analog components in a converter more complex, and this complexity causes more power to be dissipated than if a traditional approach were taken. A static calibration technique for flash analog-to-digital converters (ADCs) is discussed in this paper. The calibration is based on histogram test methods, and equivalent errors in the flash ADC comparators are estimated in the digital domain without any significant changes being made to the ADC comparators. In the trimming process, reference voltages are adjusted to compensate for static errors. Behavioral-level simulations of a moderate-resolution 8-bit flash ADC show that, for typical errors, ADC performance is considerably improved by the proposed technique. As a result of calibration, the differential nonlinearities (DNLs) are reduced on average from 4 LSB to 0.5 LSB, and the integral nonlinearities (INLs) are reduced on average from 4.2 LSB to 0.35 LSB. Implementation issues for this proposed technique are discussed in our subsequent paper,“A Histogram-Based Static-Error Correction Technique for Flash ADCs: Implementation Aspects.”

Guest Editorial: Advances in Mobile Data Communications

Sean Cai and Li Mo

2011, 9(4):  42-42. 

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Enhanced Cell-Edge Performance with Transmit Power-Shaping and Multipoint, Multiflow Techniques

Philip Pietraski, Gregg Charlton, Rui Yang and Carl Wang

2011, 9(4):  43-48. 

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In this paper, we present a technique called“fuzzy cells”that builds on the multicarrier features of Long Term Evolution-Advanced (LTE-A) and high-speed packet access (HSPA). Multiple carriers are aggregated to create a larger system bandwidth, and these carriers are transmitted at different powers by each sector antenna. This creates a set of cell-edge locations that differ from one frequency to the next. System-level simulations are performed to estimate individual user and average throughput for a hexagonal deployment of 3-sector base stations. For moderately high loads, a fuzzy cell deployment can improve tenth percentile (cell-edge) user throughput by 100% and can improve average throughput by about 30% compared with a reuse 1 scheme. Fuzzy cells reduce inter-cell interference in the same way as higher-order reuse schemes and allow users to access the full system bandwidth.

Spatial Load Balancing in Wide-Area Wireless Networks

Kambiz Azarian, Ravindra Patwardhan, Chris Lott, Donna Ghosh, Radhika Gowaikar, and Rashid Attar

2011, 9(4):  49-54. 

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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 load 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.

Uplink Power Control for MIMO-OFDMA Cellular Systems

Rongzhen Yang and Hujun Yin

2011, 9(4):  55-62. 

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In this paper, we propose a novel uplink power control algorithm, SMST, for multiple-input multiple-output orthogonal frequency-division multiple access (MIMO-OFDMA).We perform an extensive system-level simulation to compare different uplink power control algorithms, including the FPC adopted in 3GPP LTE and LTE-Advanced. Simulations show that SMST adopted in IEEE 802.16m outperforms other algorithms in terms of spectral efficiency, cell-edge performance, interference control, and trade-off control between sector-accumulated throughput and cell-edge user throughput. The SMST performance gain over FPC can be more than 40%.

Mobile Backhaul Solutions

Li Mo, Fei Yuan, and Jian Yang

2011, 9(4):  63-67. 

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In this paper, we give an overview of mobile backhaul solutions and propose an MPLS-centered solution that takes into account timing synchronization, OAM, and protection. We also propose an evolved protection bandwidth allocation mechanism that makes the transport network as efficient as possible.

Lecture Series

The Internet of Things and Ubiquitous Intelligence (4)

Dongliang Xie and Yu Wang

2011, 9(4):  68-69. 

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