It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel adaptive techniques have been deemed impractical in the past because of the problem of obtaining channel knowledge at the transmitter. The transmitter in many systems (such as those using frequency division duplexing) can not leverage techniques such as training to obtain channel state information. Over the last few years, research has repeatedly shown that allowing the receiver to send a small number of information bits about the channel conditions to the transmitter can allow near optimal channel adaptation. These practical systems, which are commonly referred to as limited or finite-rate feedback systems, supply benefits nearly identical to unrealizable perfect transmitter channel knowledge systems when they are judiciously designed. In this tutorial, we provide a broad look at the field of limited feedback wireless communications. We review work in systems using various combinations of single antenna, multiple antenna, narrowband, broadband, single-user, and multiuser technology. We also provide a synopsis of the role of limited feedback in the standardization of next generation wireless systems.

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An overview of limited feedback in wireless communication systems

LTE Release 8 is one of the primary broadband technologies based on OFDM, which is currently being commercialized. LTE Release 8, which is mainly deployed in a macro/microcell layout, provides improved system capacity and coverage, high peak data rates, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operation and seamless integration with existing systems. LTE-Advanced (also known as LTE Release 10) significantly enhances the existing LTE Release 8 and supports much higher peak rates, higher throughput and coverage, and lower latencies, resulting in a better user experience. Additionally, LTE Release 10 will support heterogeneous deployments where low-power nodes comprising picocells, femtocells, relays, remote radio heads, and so on are placed in a macrocell layout. The LTE-Advanced features enable one to meet or exceed IMT-Advanced requirements. It may also be noted that LTE Release 9 provides some minor enhancement to LTE Release 8 with respect to the air interface, and includes features like dual-layer beamforming and time-difference- of-arrival-based location techniques. In this article an overview of the techniques being considered for LTE Release 10 (aka LTEAdvanced) is discussed. This includes bandwidth extension via carrier aggregation to support deployment bandwidths up to 100 MHz, downlink spatial multiplexing including single-cell multi-user multiple-input multiple-output transmission and coordinated multi point transmission, uplink spatial multiplexing including extension to four-layer MIMO, and heterogeneous networks with emphasis on Type 1 and Type 2 relays. Finally, the performance of LTEAdvanced using IMT-A scenarios is presented and compared against IMT-A targets for full buffer and bursty traffic model.

LTE-advanced: next-generation wireless broadband technology [Invited Paper]

We present a unified analytical framework to determine the exact average symbol-error rate (SER) of linearly modulated signals over generalized fading channels. The results are applicable to systems employing coherent demodulation with maximal-ratio combining multichannel reception. The analyses assume independent fading paths, which are not necessarily identically distributed. In all cases, the proposed approach leads to an expression of the average SER involving a single finite-range integral, which can be easily computed numerically. In addition, as special cases, SER expressions for single-channel reception are obtained. These expressions reduce to well-known solutions, give alternative (often simpler) expressions for previous results, or provide new formulas that are either closed-form expressions or simple to compute numerically.

A unified approach for calculating error rates of linearly modulated signals over generalized fading channels

A base station includes: means configured to manage frequency blocks; means configured to determine, for each frequency block, scheduling information for assigning one or more resource blocks to a communication terminal being in a good channel state; means configured to generate a control channel including the scheduling information for each frequency block; and means configured to frequency multiplexing control channels within the system frequency band and to transmit it. In addition, the base station transmits the control channel by separating a non-specific control channel to be decoded by a non-specific communication terminal and a specific control channel to be decoded by a communication terminal to which one or more resource blocks are assigned.

Base station, communication terminal, transmission method, and reception method

In this paper, the performance of a prototypical IEEE 80216e network is analyzed via link and system simulations The exponential effective SIR mapping (EESM) is used to map the instantaneous SINR of received signals to a service-specific packet erasure rate (PER), which is in turn used to assess the downlink and uplink network and user data throughput A variety of data traffic models are considered, including web browsing (HTTP) and full buffer sessions, operating in flat-fading and frequency-selective multipath channels such as the ITU Pedestrian-B model The downlink network performance of the prototypical IEEE 80216e network is compared to a 3GPP UMTS high speed downlink packet access (HSDPA) system of similar physical dimensions System simulation results for the prototypical IEEE 80216e network considered show-when frequency-selective scheduling is not applied-that the IEEE 80216e downlink has similar throughput performance as HSDPA for a 70/30 TDD DL/UL frame split but approximately 40%-50% higher spectral efficiency, although control channel overhead and uplink capacity limitation remain significant open issues for further study

IEEE 802.16e system performance: analysis and simulations

The paper describes RF channel measurements conducted in a mixed urban-suburban region of Bellevue, Washington using a BPSK DS-SS sounder with a bandwidth of 20 MHz (10 Mc/s) operating in the 915 MHz ISM band. The survey was used to study delay spread characteristics in a 1.23 MHz wide channel. The fast-fading envelope distribution of resolvable rays was found to vary between Rayleigh and Rician-distributed at 1.23 MHz bandwidth. At a higher bandwidth of 20 MHz the distribution was approximately Rician with a K-factor of 8-12 dB. It was estimated that a 4-finger, 2-port non-coherent IS-95 base station would make use of the second finger pair approximately 60% of the time. The differential delay between 1st and 2nd finger assignments was usually less than 8 /spl mu/s, and there was little observable variation in the delay of the first-arriving multipath component between channel soundings spaced at 3 s intervals.

Wideband channel measurements at 900 MHz

Multi-user scheduling and OFDM techniques are well regarded as promising candidates to provide high data- rate and reliable transmissions in future communication systems. To optimally exploit multi-user diversity and frequency selectivity, exhaustive channel information is needed for every user - an impracticality given limited feedback bandwidth. Simple and efficient feedback schemes therefore become a crucial task in designing a next generation standard. In this paper, two near-optimal feedback schemes are proposed that achieve most of the multi-user scheduling benefit with very few feedback bits. It is also shown that the feedback schemes are robust to long feedback intervals. As expected, at higher Doppler spread, the performance gap using the proposed schemes becomes larger but still provides satisfactory performance.

Multi-User Scheduling for OFDM Downlink with Limited Feedback for Evolved UTRA

The impact of 'advanced' mobile receivers incorporating dual-port antenna diversity and chip-rate equalization is assessed in terms of UMTS Release-5 high speed downlink packet access (HSDPA) link and system throughput. The addition of a second antenna port to the RAKE receiver increased the link-level throughput under 3GPP RAN WG4 test conditions by 25-100%, while a chip-rate minimum mean square error (MMSE) equalizer increased throughput by approximately the same amount for the time-dispersive (Pedestrian-B) channel. Assuming ideal channel estimation, the improvement in sector throughput was between 25-90% depending on the receiver configuration. Neglecting TCP, user throughput increased 50 to 100% when either receives diversity or MMSE equalization was applied, with the throughput increase becoming 100 to 200% for the dual-port MMSE case. When TCP was included, however, user throughput improvement reduced to 20% (MMSE equalizer), 33% (dual-port RAKE) and 45% (dual-port MMSE) respectively for the same system load.

MMSE equalization for UMTS HSDPA

With the emergence of packet-based wireless broadband systems such as 802.16e, it is evident that a comprehensive evolution of the universal mobile telecommunications system specifications is required to remain competitive. As a result, work has begun on long term evolution (LTE) of the UMTS terrestrial radio access and radio access network aimed for commercial deployment in 2010. Goals for the evolved system include support for improved system capacity and coverage, high peak data rates, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operations and seamless integration with existing systems. To reach these goals, a new design for the air interface is envisioned. This paper provides a preliminary look at the air interface for Evolved UTRA (E-UTRA) and associated key technologies required to reach its design objectives. Initial E-UTRA system performance results show a 2 to 3x improvement over a reference Rel-6 UMTS system configuration [1, 2] for both uplink and downlink.

K. Stewart

Papers

IEEE 802.16e system performance: analysis and simulations

Wideband channel measurements at 900 MHz

Multi-User Scheduling for OFDM Downlink with Limited Feedback for Evolved UTRA

MMSE equalization for UMTS HSDPA

Overview of UMTS Air-Interface Evolution