The scope of this document is to define the physical layer (PHY) of the Scalable Adaptive Modulation (SAM) Wideband Air Interface (WAI). The WAI called Uw is the interface between the fixed network equipment (FNE) and a subscriber unit (SU) or directly between subscriber units in a wideband system. The general wideband system model is shown in Figure 1, and illustrates the Radio to FNE Mode of operation.

The WAI physical layer is between the Base Radio (BR) of the Fixed Station (FS) and Mobile Radio (MR) of the Subscriber Unit (SU). Alternately, it may be between the MR of one SU and the MR of a second SU, and is used for wireless communications between these functional groups. This document and the Wideband Air Interface SAM Radio Channel Coding (CHC) [1] document together make up the OSI layer 1 of the SAM WAI. Figure 2 shows the relationships between the OSI layers for the radio to FNE interface.

This document concentrates on the physical layer, whose function is to convey information through the radio frequency channel, while contending with various channel impairments such as noise, interference, radio multipath, and delay distortion. The definition of the physical layer concentrates on the following subjects:

• Modulation

• Pulsed transmission turn-on and turn-off for inbound

• Mechanism for time division multiplexing (TDM) synchronization

• Definition of TDMA frame structures

• Mechanism for amplitude and phase recovery

SAM has been designed to deliver a flexible bit rate in 50, 100, and 150 kHz radio channel bandwidths in the 700 MHz band. This flexibility permits SAM to adapt its performance by delivering higher system data throughput under good signal conditions while still supplying significantly better throughput than current systems under weaker signal conditions. The basic mode of operation for SAM is time division multiple-access (TDMA). The outbound transmission mode is continuous, while the inbound transmission mode is pulsed on a slot-by-slot basis. The number of inbound slots transmitted in by any given MR is not specified in this document. An MR may transmit in any number of inbound slots, up to the total number of inbound slots defined for the system depending upon control information from higher layers.

Layer 1 reserves certain symbols within the information stream to provide for its operation. These reserved symbols are used to synchronize to the radio channel and to provide a known reference for performing coherent demodulation of the subchannels. Many special terms used in this document are defined in the terms contained in Section 2.