to provide context. FLO is based on OFDM which is also used in DVB-H; the difference is in the size of FFT transforms. DVB-H supports 2K, 4K and 8K modes whereas FLO only supports the 4K mode. A key factor in the design of OFDM systems is the size of the transform: the number of separately modulated sub-carriers in each symbol. The FLO physical layer uses a 4K mode (yielding a transform size of 4096 sub-carriers), providing better mobile performance as compared to an 8K mode, while retaining a sufficiently long guard interval that is useful in fairly large SFN cells. FLO air interface supports the use of QPSK, 16- QAM and layered modulation techniques. In layered modulation, the data stream is divided into a base layer that all users can decode, and an enhancement layer that is decoded in areas where a higher Signal to Noise Ratio (SNR) is available. The combined use of layered modulation and source coding allows for graceful degradation of service and the ability to receive in locations or at speeds that could not otherwise have reception. Unlike DVB-H, FLO does not support 64-QAM modulation. FLO incorporates an inner code and a Reed Solomon (RS)8 outer code. Each packet contains a Cyclic Redundancy Check (CRC). 8 Reed-Solomon codes are block-based error correcting codes with a wide range of applications in digital communi- cations and storage. IMS, Services and Applications The FLO air interface employs Time Division Multiplexing (TDM) to transmit each content stream at specific intervals within the FLO waveform. The mobile device accesses overhead information to determine at which time intervals a desired content stream is transmitted. The mobile device receiver circuitry only powers up during the time periods in which the desired content stream is transmitted; at all other times it is powered down to save resources. The receiver ON/OFF duty cycle is expected to be relatively low, depending on the media content size and data rate used. 9.12.2.4.3 FLO Performance FLO can deliver 2-4 dB better performance as com