Application-layer Codec Adaptation for Dynamic Bandwidth Resource Allocation

Next generation satellite payloads must optimize the use of available spectrum to deliver the highest possible data rates while maintaining a required quality of service (QoS). The satellite channel is highly variable due to changes in the environment such as cloud cover, rain, etc. Mobile ground terminals introduce another degree of channel volatility. The dynamic bandwidth resource allocation (DBRA) technique addresses the channel dynamics by continuously monitoring key link parameters and adaptively optimizing the physical layer parameters. These modifiable parameters include: symbol rate, modulation, error correction code rate, spreading factor, transmit power, etc. A flexible radio that supports all of these parameters is coupled to a dynamic channel emulator to evaluate DBRA system performance. A complete DBRA system must also address the networking layer and even the application layer. As the satellite channel conditions change, all layers must respond appropriately to maintain QoS and avoid exceeding available data rates. Poor coordination can result in dropped calls or worse. This paper describes a DBRA testbed with multiple audio and video codecs that are selected without renegotiation. Experimental results and 'lessons learned' are presented. A brief background on modern video and audio codecs is also provided.