Coopeartive Recovery in Heterogeneous Mobile Networks

In cellular wireless networks (such as 3G net- works), multicasting/broadcasting of multimedia services greatly improves the network efficiency to distribute data to multiple recipients, taking the advantage of shared nature of the wireless medium. One challenge in providing such services is to guarantee the receiving reliability of multiple recipients, because of the error prone wireless medium and the heterogeneous channel conditions experienced by the recipients. The existing multicast/broadcast services (such as DVB, 3G MBMS) do not provide any reverse communication channel for the receivers to request the retrans- mission of lost data packets. We propose a novel method to provide QoS support by using an assistant recovery network (802.11 wireless network/MANET) to recover the loss of multicast data in the principal network (3G). In this scheme each wireless device has two interfaces: 3G and WiFi. Wireless devices are connected to a principal network to receive the multicast data. Simultaneously these wireless devices form an ad hoc assistant network and recover lost data packets cooperatively from their partner peers. Wireless devices connect to cellular networks to receive multicast/broadcast data; at the same time they form an ad-hoc recovery network to recover lost data from their peers.

Cooperative Recovery System Achitecture

A typical network system considered for cooperative recov- ery is that there are two co-existing wireless networks in an area: a principal network and an assistant network. The principal network is an infrastructure cellular wireless network with base devices. Although we consider 3G cellular network for our simulations, it may be other types of cellular net- works such as WiMax, WiFi or DVB networks. The assistant network can be an ad hoc cooperative network formed by the devices in a peer to peer architecture. As an example, the radio interface for the assistant network can be IEEE 802.11. The Cooperative Recovery system architecture is based upon the fundamental idea of using the spatial diversity and channel heterogeneity of peer devices to recover lost data frames by employing an assistant recovery network. The principal network provides downlink multicast/broadcast services from the base station to the devices. Examples of such services are video/audio streaming or other multimedia services. The assistant network helps improve the QoS and transmission reliability of the multicast services in the princi- pal network by recovering the lost data packets among peers. We assume that each wireless device is typically equipped with two physical radio interfaces. One interface is connected to the backhaul principal network and is responsible for receiv- ing the downstream multicast data from the base station/access point (principal interface). The other interface is connected to the assistant network and is used to recover the lost data frames of the principal network (assistant interface). We consider IEEE 802.11 in our Cooperative Recovery system architecture, because of its popularity and wide deployment. Wireless devices receive data from the backhaul principal network through the principal interface. At the same time they run the Cooperative Recovery protocol to dynamically form an ad hoc cooperative network via their assistant interfaces and cooperate to recover the lost multicast data frames from other peers over the assistant network. A multicast data frame is lost to a wireless device, but may be correctly received by other wireless devices due to their spatial diversity and channel heterogeneity. This recovery method improves the multicast reliability and QoS for all the involved peers by cooperation of the peers to recover the lost multicast data frames. It also helps to extend the coverage of the principal network.

The Cooperative Recovery Protocol

In order to recover the lost multicast data frames from the peers, a wireless device needs to discover, establish and maintain the partnership with the peers via the assistant network. The functionality of the protocol has three phases: Partnership Establishment, Partnership Maintenance and Data Recovery.

3. To maintain partnership by exchanging keep alive messages

4 .one or more host can be used to recover the same lost data

5. Each device organizes the data in two files:Index file and a packet file.

6. Packet file concecutively store intercepted RTP packets

7. Index file consists of two columns,packet number and packet size(indicates missing data packets)

Cooperative Recovery is almost independent of partners multicast channel condition. Therefore, no need to attract nodes with better multicast channel condition in the recovry network.

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