Naga Bhushan

Network densification: the dominant theme for wireless evolution into 5G

This article explores network densification as the key mechanism for wireless evolution over the next decade. Network densification includes densification over space (e.g, dense deployment of small cells) and frequency (utilizing larger portions of radio spectrum in diverse bands). Large-scale cost-effective spatial densification is facilitated by self-organizing networks and intercell interference management. Full benefits of network densification can be realized only if it is complemented by backhaul densification, and advanced receivers capable of interference cancellation.

LTE-Advanced: Heterogeneous networks

Long-Term Evolution (LTE) allows operators to use new and wider spectrum and complements 3G networks with higher data rates, lower latency and a flat IP-based architecture. To further improve broadband user experience in a ubiquitous and cost effective manner, 3GPP has been working on various aspects in the framework of LTE Advanced. Since radio link performance is approaching theoretical limits with 3G enhancements and LTE, the next performance leap in wireless networks will come from the network topology. LTE Advanced is about improving spectral efficiency per unit area. Using a mix of macro, pico, femto and relay base-stations, heterogeneous networks enable flexible and low-cost deployments and provide a uniform broadband experience to users anywhere in the network. This paper discusses the need for an alternative deployment model or topology using heterogeneous networks. To enhance the performance of these networks, advanced techniques are described which are needed to manage and control interference and deliver the full benefits of such networks. Range extension allows more user terminals to benefit directly from low-power base-stations such as picos, femtos, and relays. Adaptive inter-cell interference coordination provides smart resource allocation amongst interfering cells and improves inter-cell fairness in a heterogeneous network. In addition, the performance gains with heterogeneous networks using an example macro/pico network are shown.

Cell Association and Interference Coordination in Heterogeneous LTE-A Cellular Networks

Embedding pico/femto base-stations and relay nodes in a macro-cellular network is a promising method for achieving substantial gains in coverage and capacity compared to macro-only networks. These new types of base-stations can operate on the same wireless channel as the macro-cellular network, providing higher spatial reuse via cell splitting. However, these base-stations are deployed in an unplanned manner, can have very different transmit powers, and may not have traffic aggregation among many users. This could potentially result in much higher interference magnitude and variability. Hence, such deployments require the use of innovative cell association and inter-cell interference coordination techniques in order to realize the promised capacity and coverage gains. In this paper, we describe new paradigms for design and operation of such heterogeneous cellular networks. Specifically, we focus on cell splitting, range expansion, semi-static resource negotiation on third-party backhaul connections, and fast dynamic interference management for QoS via over-the-air signaling. Notably, our methodologies and algorithms are simple, lightweight, and incur extremely low overhead. Numerical studies show that they provide large gains over currently used methods for cellular networks.

CDMA2000 1/spl times/EV-DO revision a: a physical layer and MAC layer overview

This article presents key enhancements to CDMA2000 1/spl times/EV-DO systems embodied in 1/spl times/EV-DO Revision A. These enhancements provide significant gains in spectral efficiency and substantial improvements in QoS support relative to 1/spl times/EV-DO Revision 0. In particular, 1/spl times/EV-DO Revision A approximately doubles the uplink spectral efficiency and doubles the number of terminals with delay-sensitive applications that can be simultaneously supported on the system. It provides substantial reduction in latencies (approximately 50 percent) during both connection setup and the connected state. It offers comprehensive network control over terminal and application performance to enable the desired trade-offs between capacity and latency/ fairness, thereby providing full QoS support and enhanced user experience. It also provides coverage improvement (approximately 1.5 dB) relative to 1/spl times/EV-DO Revision 0. This enables operators to offer services such as VoIP, video telephony, mobile network gaming, push-to-talk, Web browsing, file transfer, and video on demand to a larger number of simultaneous users. The 1/spl times/EV-DO Revision A network can provide downlink sector capacity of 1500 kb/s and uplink capacity of 500 kb/s (two-way receive diversity) or 1200 kb/s (four-way receive diversity) with 16 active users per sector, using just 1.25 MHz of the spectrum.

Design of rate-compatible structured LDPC codes for hybrid ARQ applications

In this paper, families of rate-compatible protograph-based LDPC codes that are suitable for incrementalredundancy hybrid ARQ applications are constructed. A systematic technique to construct low-rate base codes from a higher rate code is presented. The base codes are designed to be robust against erasures while having a good performance on error channels. A progressive node puncturing algorithm is devised to construct a family of higher rate codes from the base code. The performance of this puncturing algorithm is compared to other puncturing schemes. Using the techniques in this paper, one can construct a rate-compatible family of codes with rates ranging from 0.1 to 0.9 that are within 1 dB from the channel capacity and have good error floors.

On the reverse link performance of cdma2000 1/spl times/EV DO revision A system

cdma2000 1/spl times/EV-DO release 0 (DO ReL. 0), also known as IS-856, is a third generation (3G) wireless solution to providing wide-area high-speed mobile Internet access. cdma2000 1/spl times/EV-DO revision A (DO Rev. A) system provides enhancements to DO Rel. 0, such as higher spectral efficiency and advanced quality-of-service (QoS) support. In this paper we evaluate the reverse link performance of DO Rev. A system from a physical layer perspective. Specifically, we obtain DO Rev. A reverse link capacity via analysis as well as system simulations with complete modeling of physical- and MAC-layer dynamics. We show that DO Rev. A achieves significant capacity gain over DO Rel 0 in supporting delay-sensitive applications and provides flexible tradeoff in delay, capacity and physical-layer error-rate performance based on QoS requirement. Under moderate sector loading, DO Rev A achieves a reverse link sector capacity on the order of 600-700 kbps with two receiving antennas, i.e. a two-to-three fold improvement over DO Rel 0, while using the same 1.25 MHz of spectrum. Furthermore, sector throughput on the order of 1.2 Mbps is achievable with four receiving antennas, in the form of spatial array or pairs of cross-polarized (X-pol) antennas.

Reverse traffic channel MAC design of cdma2000 1xEV-DO revision A system

cdma2000 1xEV-DO (DO), also known as IS-856, is a third generation (3G) wireless solution providing high-speed mobile Internet access. cdma2000 1xEV-DO revision A (DO-RevA) system provides further enhancements to DO, such as higher system capacity and advanced quality-of-service (QoS) support In this paper we motivate and describe the design of the reverse link traffic channel MAC (RTCMAC) of DO-RevA system, which uses a novel combination of centralized specification of flow behavior together with autonomous mobile packet allocation subject only to resource congestion control. We demonstrate that RTCMAC achieves full resource allocation flexibility through an efficient robust design, well suited to the CDMA reverse link.

Optimal Resource Allocation for Data Service in CDMA Reverse Link

The optimal resource allocation policy is studied for non-real-time users in CDMA reverse link. The resource allocation policy of interest includes channel coding, spreading gain control and power allocation under the conventional receiver operation. The constraints in the optimization include peak transmit power of the mobile station, total received power at the base station and QoS in the form of minimum SINR for each user. The coding and spreading gain control can be separated from the power allocation strategy. Our results show that the optimal power allocation policy depends on the objective function: a greedy policy is optimal to maximize the sum of throughput from each user, whereas a fair policy is optimal to maximize the product of throughput from each user. A unified approach is taken to derive the optimal policies, and it can also be applied to other power allocation problems in CDMA reverse link. Numerical results of the channel capacity are presented for both objectives along with the effect of QoS constraints.

Distributed Interference Management and Scheduling in LTE-A Femto Networks

We design novel mechanisms and algorithms for fast, simple, and distributed interference management and scheduling in wireless femto networks via exchange of information over-the-air (OTA). We focus on the Long Term Evolution (LTE) of the 3GPP standard and on the downlink; we leverage the existing signalling and delineate additional signals that need to be introduced in the standard. Key aspects of our work include: (1) our design involves only one round of exchange of very few bits of information in each time slot (of the order of 1 ms) resulting in a very low control overhead, (2) our algorithm is a heuristic derived from the maximum weight scheduling algorithm for a realistic interference model (as opposed to an abstract

Impact of Coordination Delay on Distributed Scheduling in LTE-A Femtocell Networks

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