UTRAN long term evolution is currently being standardized in 3GPP with the aim of more than twice the capacity over high-speed packet access. The chosen multiple access for uplink is single carrier FDMA, which avoids the intra-cell interference typical of CDMA systems, but it is still sensitive to inter-cell interference. As a result, the role of the power control becomes decisive to provide the required SINR, while controlling at the same time the interference caused to neighboring cells. This is the target of the fractional power control (FPC) algorithm lately approved in 3GPP. This paper evaluates in detail the impact of a FPC scheme on the SINR and interference distributions in order to provide a sub-optimal configuration tuned for both interference- and noise-limited scenarios.

Performance of Uplink Fractional Power Control in UTRAN LTE

In this study we analyze the downlink OFDMA system level performance for three different channel quality indicator (CQI) reporting schemes. The effect of terminal measurement and estimation errors, quantization from formatting and compression, and uplink reporting delays and detection errors are included. We find that a simple threshold-based CQI scheme provides an attractive trade-off between downlink system level performance and uplink CQI signaling overhead, as compared to using a best-M scheme. When applied to the UTRAN LTE system in a 10 MHz bandwidth, we find that a frequency domain packet scheduling gain of 40% is achievable with a CQI word size of only 30-bits. Finally, the effect of applying a so-called outer loop link adaptation algorithm is reported.

Frequency Domain Scheduling for OFDMA with Limited and Noisy Channel Feedback

3GPP has recently agreed on an Open Loop Power Control (OLPC) for the uplink in UTRAN Long Term Evolution. The power control configuration determines the level of interference in the system, but requires to be tuned depending on the propagation scenario, user's bandwidth, etc. A reliable knowledge of the interference would be very useful for the operator to determine the maximum link budget for a certain coverage performance. In this paper we propose a novel algorithm to use the Overload Indicator for an automatic adjustment of the OLPC parameters to achieve the desired interference operating point, showing its potential compared to an a priori setting.

Uplink Interference Control in UTRAN LTE Based on the Overload Indicator

Evolved (E-) UTRA is currently being standardized as a long term evolution (LTE) of the 3GPP radio access technology. One of the goals of E-UTRA is to achieve 2-4 times the spectral efficiency and user throughputs compared to HSUPA/HSDPA. Support for fast link adaptation based on adaptive modulation & coding (AMC) is one of the features being introduced in the E-UTRA specifications to enhance the uplink spectral efficiency. This paper focuses on the performance evaluation of fast AMC in E-UTRA uplink compared to link adaptation schemes that only slowly adapt to the varying channel and interference conditions. It is shown that despite measurement errors and the high variability of uplink inter-cell interference, fast AMC can boost the capacity of E-UTRA uplink by approximately 20% to 25%.

Performance of Fast AMC in E-UTRAN Uplink

In this paper, we evaluate the tradeoff between the amount of uplink channel feedback information and the orthogonal frequency-division multiple access (OFDMA) downlink performance with opportunistic frequency-domain packet scheduling. Three candidate channel feedback schemes are investigated, including practical aspects, such as the effects of terminal measurement errors, bandwidth measurement granularity, quantization, and uplink signaling delays. The performance is evaluated by means of system-level simulations with detailed modeling of various radio resource-management algorithms, etc. Our results show that the optimal tradeoff between the channel feedback and the downlink OFDMA system performance depends on the radio channel frequency coherence bandwidth. We conclude that the so-called average best-M scheme is the most attractive channel feedback solution, where only the average channel quality for the best M subbands is reported, together with a bit mask identifying those subbands. The latter scheme only has a channel feedback word size in the range of 10-20 bits for the considered OFDMA system with 10-MHz bandwidth.

Performance Analysis of Simple Channel Feedback Schemes for a Practical OFDMA System

The joint third-generation system performance of high-speed downlink packet access (HSDPA) and Release 99 (Rel'99) dedicated channels (DCH) is studied. Given such a scenario, the optimal sharing of the cell carrier transmit power between HSDPA and DCH, which is conditioned on a certain number of channelization codes that are reserved for HSDPA transmission, is addressed. Detailed network-performance results are shown from a comprehensive dynamic system-level simulator, which includes a simulation of many cells and users, and a detailed modeling of layer 1 to layer 3. Compared to a scenario without HSDPA, the total cell throughput can be increased by 69% by allocating five high-speed physical downlink shared channel codes and 35% of the maximum cell transmit power to HSDPA transmission. These results are obtained for a macrocellular scenario with best effort packet data services. Furthermore, it is demonstrated that part of this capacity gain comes from better utilization of the available cell transmit power since less power control headroom must be reserved for HSDPA. The presented performance results reflect the expected performance improvement from gradually introducing HSDPA in an existing Rel'99 wideband code-division multiple-access network

T.F. Lootsma

Papers

Performance of High-Speed Downlink Packet Access in Coexistence With Dedicated Channels