Adaptive TDMA/OFDMA for Wide-Area Coverage and Vehicular Velocities.

Mikael Sternad, Uppsala University
Sorour Falahati, Uppsala University
Tommy Svensson, Chalmers Univ. of Technology and
Daniel Aronsson, Uppsala University.

IST Summit, Dresden, June 19-23 2005.

Outline:

Adaptive communication systems allocate (schedule) time, frequency and antenna resources based on channel quality and user requirements. They enable efficient resource utilization and multi-user scheduling gains, when channels to different terminals fade independently.

In systems based on time division multiple access/ adaptive OFDM (TDMA/OFDMA), time-frequency resources (chunks) are allocated. This provides a flexible small-scale granularity of the resources, ideal for transmitting small as well as large packets.

Based on the results obtained within the Swedish Wireless IP project, we are assessing the feasibility of such methods in novel broadband radio interfaces within the EU FP6 Integrated Project WINNER. We here investigate adaptive downlinks and uplinks based on fast scheduling and link adaptation, also for users at vehicular speeds, with a non-adaptive fall-back mode for very fast moving users. The non-adaptive fall-back mode design is outside the scope of this paper, but should be based on time, frequency and space diversity techniques.

Allocation of fast fading channels requires channel prediction. The signal to interference and noise ratio (SINR) is to be predicted for all potential resources in future transmission. In the proposed downlink, each terminal predicts the SINR over a major part of the total bandwidth. All active terminals report source coded SINR values or source coded suggested modulation formats over a shared uplink control channel. A resource scheduler, located close to one or several radio access points, allocates the downlink resources.

Abstract:

Within the EU FP6 Integrated Project WINNER, adaptive transmission is investigated as a key technology for boosting the spectral efficiency of a new radio interface for 4G systems. Adaptive allocation of time-frequency chunks in an OFDM-based system offers a significant potential, but also poses challenges.

Within work package two of WINNER, we study critical issues such as the feasibility of adaptive transmission over fading downlink/uplink channels to/from vehicular terminals, the corresponding required channel prediction accuracy, and the required feedback control bandwidth. This paper summarizes recent results obtained within WINNER, and related results obtained within the Swedish Wireless IP project.

Related publications:

Proc. of the IEEE (Dec. 2007) invited paper on adaptive transmission in beyond-3G wireless systems, with later results.

Improved results by modfied coding schemes (VTC06-Spring).

Adaptive modulation systems for predicted wireless channels. IEEE TCOM 2004 paper presenting the method for adjusting modulation rate limits.

Channel Power Prediction, by using unbiased predictors and advanced regressor noise reduction (VTC 2002-Fall).

PhD Thesis on channel prediction, by Torbjörn Ekman.

Paper 1 at VTC2003, on adaptive modulation, multiuser diversity and channel variability within bins.

Paper 2 at VTC2003, on the OFDM downlink and cell planning for high SIR.

Paper 3 at VTC2003, on OFDM downlink channel estimation and channel prediction.

Paper 4 at VTC2003, on the impact of prediction errors on the adaptive modulation.

Source:

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