Tamer Kadous

Extending LTE to unlicensed band - Merit and coexistence

Innovations enabling efficient spectrum utilization is a key element to optimize user experience with growing data demand. This paper discusses the approach of extending enhancements in cellular technology like LTE to unlicensed band for higher spectral efficiency and better user experience. A key challenge for such extension is the coexistence with legacy technology such as Wi-Fi. The description herein highlights techniques for effective coexistence. The results include evaluation and lab data that demonstrate how the technology provide benefit to surrounding Wi-Fi deployment and contribute towards enhancing spectral efficiency of the unlicensed band.

Ordered H-BLAST for MIMO/OFDM systems over multipath channels

This paper addresses an OFDM/MIMO coded system where multiple data sub-streams are encoded separately and transmitted in parallel. If successive interference cancellation (SIC) across sub-streams is to be used at the receiver, to minimize error propagation (EP), it is recommended to decode a full sub-stream before cancellation to utilize the powerfulness of channel coding. For the same reason, it is also recommended to process the different sub-streams in an order that matches their reception quality. While this is always possible in flat fading channels, it is not straightforward in multipath channels where different modulation symbols have different channel qualities due to frequency selectivity. This paper addresses this problem and introduces an ordering scheme for coded systems that significantly improves system performance.

Field Results on MIMO Performance in UMB Systems

The paper presents MIMO field performance results observed using a ultra mobile broadband (UMB) testbed network. We evaluate metrics such as antenna correlations and channel condition number to characterize the MIMO channel. Results show that low condition numbers, which are beneficial to MIMO, are prevalent for a majority of the coverage area in our network. We demonstrate that the use of MIMO provides gains of the order of 20-40% over SIMO transmissions. These gains are made possible by the use of cross-polarized transmit antennas and advanced UMB features that allow dynamic MIMO vs. SIMO transmission selection based on channel conditions. These results are obtained in a truly mobile, wireless wide-area deployment, which makes them unique. Our results point to the viability and value of MIMO in future mobile wireless networks.

Multi-antenna Techniques in Ultra Mobile Broadband Communication Systems

Theoretically, multi-antenna techniques offers significant capacity benefits, but realizing these gains in deployed wireless systems remains a very challenging problem. MIMO has been used in wireless LAN systems with great success. However, due to the hugely varying spatial profiles and velocity patterns of the access terminals, integrating MIMO techniques in a wireless WAN system has been a difficult design problem. This paper introduces the design paradigms of Ultra-Mobile Broadband, which is poised to become the successor of EVDO as the next generation of high speed wireless system. UMB allows the use of MIMO in various forms to suit the deployment scenario, and elicit as much gain as possible.

WLC36-3: Selective Virtual Antenna Permutation for Layered OFDM-MIMO Transmission

In this paper we introduce selective virtual antenna permutation (S-VAP) for layered OFDM-MIMO transmission in downlink cellular environments. In the S-VAP scheme, the base station spatially permutes multiple independently encoded layers and then transmits the permuted layers over selected virtual antennas. The mobile station employs a successive interference cancellation (SIC) based receiver to maximize the spectral efficiency. The layer permutation enables a significant reduction of channel quality feedback information necessary to adjust the data rate of each layer. Transmission over selected virtual antennas instead of physical antennas enables efficient power amplifier utilization and thus brings out a quantized spatial water-filling gain.

COSFA: an efficient spatial multiplexing scheme for rate adaptive systems

This paper introduces OFDM/MIMO architecture for rate adaptive systems denoted by COSFA. We assume multiple codeword transmission and use successive interference cancellation (SIC) at the receiver to decouple the different data sub-streams. The maximum data rate on each sub-stream as well as the number of data sub-streams, for particular channel realization, are predicted by the receiver and fed back to the transmitter. COSFA is designed to fit rate adaptive systems that can encounter wide range of SNR and channel conditions. It captures both the diversity and spatial multiplexing (SM) modes of the channel in one design. Moreover, COSFA is a power-efficient architecture since its inherent design allows full power utilization for any number of data sub-streams - a desirable feature in rate adaptive systems.

Multi-Antenna Techniques for Evolved 3G Wireless Communication Networks: An Overview

Multi-antenna techniques offers significant capacity benefits. But realizing these gains in practical wireless systems remains a very challenging problem. MIMO-OFDM has been used in wireless LAN systems with great success. However, due to the largely varying spatial profiles and velocity patterns of the access terminals, integrating MIMO techniques in a wireless WAN system has been a difficult design problem. This paper overviews the multi-antenna techniques used in evolved 3G wireless communications systems, such as 3GPP2 Ultra-Mobile Broadband (UMB), IEEE Mobile Broadband Wireless Access (MBWA) and 3GPP LTE, which are poised to become the successor of 3G systems, e.g., 3GPP2 1xEVDO and WCDMA, as the next generation of high speed wireless system. This paper uses MIMO in various forms to suit the deployment scenario. Although we use UMB as a design paradigm in this paper, most of the results apply to OFDM systems in general.

MIMO in wireless WAN — the UMB system

Theoretically, MIMO offers significant capacity benefits, but realizing these gains in deployed wireless systems remains a very challenging problem. MIMO has been used in wireless LAN systems with great success. However, due to the hugely varying spatial profiles and velocity patterns of the access terminals, integrating MIMO techniques in a wireless WAN system has been a difficult design problem. This paper introduces the design paradigms of ultra-mobile broadband, which is poised to become the successor of EVDO as the next generation of high speed wireless system. UMB allows the use of MIMO in various forms to suit the deployment scenario, and elicit as much gain as possible.

Interference-aware rate control for bursty interference channels

Interference in wireless networks has been identified as one of the main hurdles towards achieving higher network capacity. However, most of the literature has focused on solving interference problems assuming that interference is non-bursty. In this paper, we study bursty interference channels and propose novel interference-aware rate control algorithms. The proposed algorithms include single and multi-layer transmission schemes. We also present a framework for optimizing rate selection so that the overall throughput is maximized. Significant performance gains relative to traditional Hybrid Adaptive Repeat reQuest (HARQ) schemes are demonstrated.