This post covers WIRELESS COMMUNICATIONS AND NETWORKS by William Stallings.

Basic Ideas

• Baseband Specification

• Concerned with connection establishment in a piconet, addressing, packet format, timing, and power control.

• Frequency Hopping: Frequency hopping (FH) in Bluetooth serves two purposes:

  

  • It provides resistance to interference and multipath effects.
  • It provides a form of multiple access among co-located devices in different piconets.

• The FH scheme works as follows. The total bandwidth is divided into 79 (in almost all countries) physical channels, each of bandwidth 1 MHz. FH occurs by jumping from one physical channel to another in a pseudorandcm sequence.

• The same hopping sequence is shared by all of the devices on a single piconet; we will refer to this as an FH channel2

• The hop rate is 1600 hops per second, so that each physical channel is occupied for a duration of 0.625 ms. Each 0.625 ms time period is referred to as a slot, and these are numbered sequentially.

• Bluetooth radios communicate using a time division duplex (TDD) discipline.

• TDD is a link transmission technique in which data are transmitted in one direction at a time, with transmission alternating between the two directions.

• Because more than two devices share the piconet medium, the access technique is TDMA.

• Thus piconet access can be characterized as FH-TDD-TDMA.

• In the figure, k denotes the slot number, and f(k) is the physical channel selected during slot period k.

• Transmission of a packet starts at the beginning of a slot. Packet lengths requiring 1,3, or 5 slots are allowed.

• For multislot packets, the radio remair s at the same frequency until the entire packet has been sent. In the next slot after the multislot packet, the radio returns to the frequency required for its hopping sequence,

• So that during transmission, two or four hop frequencies have been skipped

• Using TDD prevents crosstalk between transmit and receive operations in the radio transceiver, which is essential if a one-chip implementation is desired.

• Note that because transmission and reception take place at different time slots, different frequencies are used.

• The FH sequence is determined by the master in a piconet and is a function of the master’s Bluetooth address. A rather complex mathematical generation involving permutations and exclusive-OR (XOR) operations is used to generate a pseudorandom hop sequence.

• Because different piconets in the same area will have different masters, they will use different hop sequences. Thus, most of the time, transmissions on two devices on different piconets in the same area will be on different physical channels.

• Occasionally, two piconets will use the same physical channel during the same time slot, causing a collision and lost data.

• However, because this will happen infrequently, it is readily accommodated with forward error correction and error detection ARQ techniques. Thus, a form of code division multiple access (CDMA) is achieved between devices on different piconets in the same scatternet; this is referred to as FH-CDMA.