Recently, digital video broadcasting-handheld (DVB-H) and IP datacast over DVB-H (DVB-IPDC) have been developed to support broadcasting services. DVB-H is designed to support digital video broadcast for handheld devices, whereas DVB-IPDC can integrate with an IP-relay network to complement the data loss problem in DVB-H. Assuming that WiMAX networks are adopted to support DVB-IPDC, this paper points out two critical problems: group packet loss (GPL) and broadcast data handover (BDH). GPL occurs when there is a burst of retransmission requests for the same pieces of data with high spatial or temporal correlation. BDH happens when some devices that made the above requests handover to new serving cells. To solve these problems, we propose lazy wait and group acknowledgement schemes to alleviate duplicate requests by exploiting their spatial and temporal correlations. This not only reduces the requests submitted by neighboring devices in both space and time domains but also avoids handovering devices from sending duplicate requests in new cells. Through mathematical analysis, we show how to adaptively adjust the timers of lazy wait and group acknowledgement based on channel quality. Simulation results prove that our schemes can efficiently reduce retransmission requests and retransmission packets, thus alleviating congestion in the IP-relay network.
- data recovery
- wireless network