Antenna-sector time-division multiple access for broadband indoor wireless systems

Abstract

Abstract-This paper investigates a hybrid space-time-division multiple access (S-TDMA) for broadband indoor wireless systems using sectored antennas. It is shown that portables which are located in different sectors of an indoor microcell may be able to reuse the same frequency and the same time slot. However, this requires careful scheduling of packet transmissions in order to avoid transmitting packets that would jam each other during the same time slot. It is proposed that the scheduling be performed in the base station, i.e., a central control architecture. The optimum scheduling algorithm, the one that maximizes the number of packets transmitted per frame, may be in the NP-complete class of problems, so it cannot be solved in real time. Therefore, a suboptimum algorithm, called the first fit algorithm (FFA), is proposed for frame scheduling. It was found that the capacity gain achieved by the FFA is dependent on the capture threshold, which is defined as the minimum signal-to-interference ratio required in order to achieve a given packet error rate goal. The capture threshold depends on the modulation and coding schemes. This paper investigates the performance of the FFA operating with multicarrier trellis-coded modulation. An alternative multicarrier modulation is analyzed, and the FFA performance is investigated when operating with the alternative and with the conventional multicarrier through computer simulations based on measured data which were obtained with a sectorization level of ten (using ten antenna sectors in the base station). The simulations have shown that the FFA can provide a large capacity gain when operating with multicarrier trellis-coded modulation and using differential detection. For example, while previous schemes can transmit only one packet at a time, the proposed scheme can transmit, on average, more than four packets per time slot in an open indoor location, or close to three packets per time slot in a closed indoor location with internal walls of concrete blocks.Index Terms-Broadband communication, directive antennas, frequency division multiplexing, indoor radio communication, space division switching, time division multiaccess, trellis coded modulation, wireless LAN.

Multiuser MAC Schemes for High-Throughput IEEE 802.11n/ac WLANs

“…An early work proposes the first-fit algorithm, a sub-optimum but less complex scheduling method that selects sets of packets that can be transmitted simultaneously [20]. However, one of the basic assumptions of this work is that the channel between the base station and the users is quasi-static and is considered known by the base-station, whereas scenarios with varying channel conditions are left for future consideration.…”

On the capacity and scheduling of a multi-sector cell with co-channel interference knowledge

“…However, such difficult scenarios can be addressed by the space division multiple access (SDMA) approach addressed in this paper, where directional antennas are used to sub-divide the cell into sectors that reuse bandwidth. The advantages of such an approach has been noted before [7], [11] and in principle it can be relatively simple to implement since it does not require any major modification to end user devices and/or has changes mostly constrained to the media access control layer of the wireless network. However, careful control of co-channel interference in such scenarios is required as is the need for efficient and fast scheduling, especially in time varying fading environments typical of mobile wireless.…”

“…A similar study [1] also considers a hexagonal cellular structure but shows that packet error rate and delay can be reduced by coordinating transmission amongst collinear, same frequency sectors located in adjacent cells. The importance of coordinating interfering signals is further shown in [7] where the operation of a single 10-sectored cell is simulated. The work indicates that high throughput is achievable with a heuristic centralized scheduling scheme if the base station has interference information from the remote units.…”

Practical bit loading schemes for multi-antenna multi-user wireless OFDM systems

“…they assume that only a finite set of beamvectors is available. A related concept based exclusively on power capture threshold is [18] for a sectorized AP. However, to the best of our knowledge, the normalized scalar product has not been yet shown to be a suited technique to separate the users.…”