 has no knowledge of the location of Radio B or any other radio in the network. Networks Figure 2.5. (continued) Assume all other radios have a common key that generates a common pseudorandom sequence used for spread-spectrum signalling. Radio A transmits the message in an omni-directional signal that also identifies the destination Radio B and source Radio A. This signal can be received by all radios within some range, assuming all radios use the common key. The pro- tocol for radios in this network is to retransmit the same message only once right after first receiving it. Hence, as shown in Figure 2.5(a), Radio A first transmits the message. In Figure 2.5(b) only radios marked in dark first receive Radio A's transmission and retransmit the same message. In Figure 2.5(c) radios that received the signal for the first time in the second trans- mission are shown. These in turn retransmit the same message with the final result that Radio B receives the message as shown in Figure 2.5(d). Retransmissions, however, may continue until each radio has received and transmitted the message once. In this flooding technique a single radio may receive the same signal simul- taneously from several other radios. This is the same as receiving a signal Multiple Access from a single transmitter in a multipath channel. If the relative delays between the different signals are greater than a "chip" time, then the receiver can resolve this difference and detect only one signal. Typically, in mobile digital radio systems real multipath would occur and techniques for handling it are required (see Chapter 1, Part 2). There are several variations of the flooding scheme [3], [5]-[7]. For instance, each radio may retransmit the same message more than once. However, a maximum number of hops for a flooding signal might be set requiring each retransmission to update a "hop count" which is also trans- mitted. If a radio receives a signal with a count equal to a predetermined value, it will not retransmit it. Another approach is for each radio t