Field Measurements with a 5.25 GHz Broadband MIMO-OFDM Communication System

Theoretical capacity calculations and corresponding simulations show significant capacity/throughput gains from MIMO systems. Whether these gains are achievable in a real system, deployed in a practical environment, depends on a variety of factors, such as the choice of the communication algorithms, analog impairments and the "quality" of the wireless channel to sustain MEMO communications. In this paper, a 5.25 GHz broadband MIMO-OFDM testbed is described along with field measurements conducted with it. The MIMO-OFDM communication algorithms and also the impact of analog impairments on the performance of the system are described. Detailed system calibration results are described which serve as a baseline for results of field measurements. The results of wireless measurements are compared with the theoretical capacity, computed with the channel estimates obtained during the demodulation process. The average achievable capacity in the indoor wireless environment is shown to be 9.97 bps/Hz (bits per sec per Hz) while the capacity loss due to analog impairments and the choice of algorithms is about 2.33 bps/Hz. Also, field measurements conducted with the system in various environments are presented comparing the average throughput/capacity achieved in each of these environments.     

Low BER Performance Estimation of LDPC Codes via Application of Importance Sampling to Trapping Sets

We introduce an importance sampling (IS) method that successfully simulates the performance of Low density Parity Check (LDPC) Codes in an AWGN channel at very low bit error rates (BERs). By effectively finding and biasing bit node combinations that are the dominant sources of error events, called trapping sets, the developed technique provokes more frequent decoder failures. Consequently, fewer simulation runs and higher simulation gains are achieved.     

A reconfigurable 8 GOP ASIC architecture for high-speed datacommunications

A flexible and reconfigurable signal processing ASIC architecture has been developed, simulated, and synthesized. The proposed architecture compares favorably to classical DSP and FPGA solutions. It differs from general-purpose reconfigurable computing (RC) platforms by emphasizing high-speed application-specific computations over general-purpose flexibility. The proposed architecture can he used to realize any one of several functional blocks needed for the physical layer implementation of data communication systems operating at symbol rates in excess of 125 Msymbols/s. Multiple instances of a chip based on this architecture, each operating in a different mode, can be used to realize the entire physical layer of high-speed data communication systems. The architecture features the following modes (functions): real and complex FIR/IIR filtering, least mean square (LMS)-based adaptive filtering, discrete Fourier transforms (DFT), and direct digital frequency synthesis (DDFS) at up to 125 Msamples/s. All of the modes are mapped onto a common, regular data path with minimal configuration logic and routing. Multiple chips operating in the same mode can be cascaded to allow for larger blocks     

An adaptive weaver architecture radio with spectrum sensing capabilities to relax RF component requirements

This paper presents an architecture that utilizes spectrum sensing with a Weaver architecture receiver to ease the requirements on the RF front-end components. With the ability to sense the environment, large interferers that overwhelm small desired signals can be avoided. The learning and adapting capabilities are enabled by means of a flexible receiver architecture employing variable local oscillators (LOs) at RF and intermediate frequency (IF). Avoiding large interferers can reduce image rejection ratio (IRR) requirements for a given performance and results in a greater tolerance to the Q of filters and receiver mismatches. The design approach is applied to an IEEE 802.11a receiver and the results show that for a given performance level, the proposed design requires an IRR that is 40 dB less than that required for conventional Weaver receivers     

Adaptive link layer strategies for asymmetric high-speed wirelesscommunications

A forward error correction (FEC) strategy and a medium access control (MAC) protocol that are thoroughly tailored to complement and support a high-speed asymmetric physical layer design based on equalization and precoding is presented and fully discussed. Both proposals exhibit a high degree of adaptability and flexibility, which allows for increased data throughput while providing a wide range of quality-of-service requirements. Fast link layer adaptation is made possible through the joint design of link and physical layers. The adaptive FEC algorithm is based on the use of variable-rate trellis coded modulation with fast channel estimation, while the MAC protocol employs a centralized, dynamic slot allocation technique. The overall system design is shown to achieve high spectral efficiency, while minimizing energy consumption at the portable unit     

Chemical studies of the oil from pistacia nuts growing wild in iran

Large populations of Pistacia grow wild in dif-ferent parts of Iran. The fruits of two species, namely,Pistacia atlantica Subsp.mutica andP. atlantica Subsp.kurdica are consumed by the natives because of the high content of oil in kernels and outer skin layers. The kernels of both species are rich in oil (over 50%), and the oil content in the outer skin layer ofP. atlantica Subsp.kurdica is 63% and in the other variety 30%. Unsaponifiable matter and fatty acid compositions of the oils were determined and the results compared with the oil fromPistacia vera L.     

Asymmetric physical layer design for high-speed wireless digitalcommunications

High data rates and portability are conflicting requirements in the design of reliable indoor wireless data communication systems. Asymmetric system design addresses this problem by exploiting the major differences in the availability of resources (i.e., energy, space) that exist between base stations and portable units. Such an approach seeks to concentrate most of the signal processing tasks involved in the operation of the two-way wireless link at the base station. This paper presents and discusses the implications of a set of techniques for asymmetric physical layer system design based on the use of channel precoding for forward transmission. System performance is assessed via simulations using a realistic time-varying channel model. Simplified two-way antenna diversity implemented exclusively at the base station and the key issue of automatic gain control at the receive side of the precoded link are also addressed and evaluated. Simulation results confirm that the adoption of these techniques enables reliable digital communication at a data rate of 20 Mbit/s on both links while significantly reducing the power consumption of the portable unit     

Simulation,implementation and performance evaluation of a diversity enabled WCDMA mobile terminal

Smart antenna array technology has been shown to greatly improve the performance of wireless communication systems. In this article, we describe the impact of smart antenna array processing at the mobile terminal for Wideband Code Division Multiple Access (WCDMA) cellular networks. Using system simulations we demonstrate the quality of service, network coverage, and network capacity improvement provided by a WCDMA dual antenna receiver and we establish a relationship between this improvement and the link level performance. We then describe a receiver architecture for a dual antenna WCDMA mobile receiver. The proposed receiver was implemented, as part of a complete mobile terminal solution, in an ASIC using a 0.18 μm, 1.8 V CMOS technology. The ASIC was integrated with RF, analog and digital components in a PCMCIA card form factor. The PCMCIA is a 3GPP compliant user equipment and has been submitted to standardized performance and conformance tests. Experimental measurements gathered with the PCMCIA card illustrate the impact of a diversity enabled mobile data terminal on the link level performance. For various propagation environments and transmission data rates, improvements in the range of 2.7 – 10 dB in the required DPCH I _c/I _or for a 1% Block Error Rate (BLER) were observed. These measurements are within 1.4 dB of the ideal link level simulations which indicates that the predicted improvement at the network level should also materialize. The results presented in this paper show the tremendous potential of smart antenna arrays in 3G WCDMA cellular networks and establish diversity as a viable solution for high-speed cellular communications.     

Design and development of a 5.25 GHz software defined wireless OFDM communication platform

With growing interest in broadband wireless communication systems, a research platform for evaluating various communication schemes becomes essential. Such a system can be used to validate the assumptions and results of various theoretical and simulation-based studies. This article discusses the design and development of a multicarrier multi-antenna software defined radio, operating at 5.25 GHz in a 25 MHz bandwidth. The calibration process is described in detail along with a discussion of all the issues such as I/Q mismatch and phase noise that degrade and limit the performance of the system. Hardware and software solutions to these problems are described. Results of the calibration process and wireless experiments on the system are presented as well.     

Analog Impairments in MIMO-OFDM Systems

MIMO-OFDM is being considered for communication systems where high throughput and spectral efficiency are important factors. Analog impairments like I/Q mismatch and phase noise significantly degrade and limit the performance of communication systems. In this paper, we analyze the impact of I/Q mismatch and phase noise in MIMO-OFDM systems as a function of the number of antennas. We show the improvement in performance that is possible when these impairments are cancelled. We also discuss the impact of correlated and uncorrelated phase noise in MIMO-OFDM systems. Finally, we show the results of I/Q mismatch and phase noise cancellation in wireless measurements performed using a 2times2 MIMO-OFDM testbed