Parallel PPDU Transmission Mechanism for Wideband Wireless LANs

Abstract

When the preambles of a wideband 802.11n/ac frame transmission are affected by a collision with a 20MHz frame on one of the subchannels, a receiver might fail to decode the whole wideband frame. Experimental evaluations with off-the-shelf 802.11n hardware showed that the vulnerability of wideband frame transmission to a narrowband collision/interference is a real problem. To mitigate the severe impact of narrowband collision/interference on wideband transmission, we propose to transmit several 20MHz frames in parallel instead of a single wideband frame so that a narrowband collision on one of the subchannels affects only the parallel frame transmitted on that subchannel. Performance evaluations demonstrated that the proposed parallel frame transmission scheme significantly improves the throughput and delay performance of wideband transmissions under different traffic and channel conditions. While the throughput performance of the proposed scheme for saturated traffic conditions was analytically validated, extensive simulation-based evaluations showed that the proposed scheme achieves great performance improvement for unsaturated traffic conditions and hidden node environment. INDEX TERMS 802.11, wireless local area network (WLAN), channel bonding, wide channel access, parallel transmission, narrowband collision.

Performance Analysis of Aggregation-Enabled IEEE 802.11 WLANs With Variable Aggregation Size

“…Hajlaoui et al [6] proposed an algorithm that adapts the MPDU size for noisy channel and adjusted Bianchi's model to analyze the performance for a saturated traffic condition. Seytnazarov et al [7] proposed a scheme to transmit multiple 20MHz PHY PDUs (PPDUs) in parallel instead of a single wideband PDU and analyzed the performance of the scheme using Bianchi's model. The authors in [10] and [11] proposed new automatic repeat request (ARQ) schemes and analyzed their throughput performance with a fully saturated traffic assumption.…”

“…All the above modeling approaches for aggregationenabled WLANs consider a fully saturated traffic condition where every station has enough packets to compose an A-MPDU of maximum aggregation size [4]- [7] or the aggregation size that the considered ARQ scheme currently allows [8]- [13]. However, some performance modeling attempts include unsaturated traffic conditions.…”

“…Note that it may be intractable to get a closed-form expression of steady-state probabilities because the collision probability p depends on these steady-state probabilities being recursively expressed by p. On the other hand, the drop possibility of an A-MPDU is expected to be very small, because it needs to collide r + 1 times successively. Furthermore, just after such an infrequent drop event, the station selects the backoff counter 0 with probability 1/W 0 , and thus, the second term on the right side of ( 7) has negligible values for reasonable values of p. To obtain a closed-form expression, we approximate ( 6) and ( 7) by removing the second term on the right side of (7) and adding it to (6). Now, the equations for π n,0 * and π n,0,0 are updated as follows.…”

“…Those works can be divided into two categories. The works in the first category assume that all stations always have the necessary number of packets in their buffers to compose and send A-MPDU of maximum aggregation size [4]- [7]. The models in the second category assume that the stations always have enough packets to compose and send the A-MPDU of the aggregation size that the considered ARQ scheme currently allows [8]- [13].…”