TABLE OF CONTENTS Spread spectrum techniques involve ways of increasing the bandwidth of a transmitted data stream beyond the minimum transmission bandwidth indicated by the data rate. These techniques are prime candidates for wireless distance measuring because they provide a platform for attaining ranging accuracy which is larger than that commonly achieved on narrow band systems with comparable data rates.
In Chapter 2, two spectrum spreading methods were described: chirp and direct sequence. Other methods are frequency hopping and time hopping, as well as combinations of the four. This chapter deals with direct sequence spread spectrum. Frequency hopping and time hopping spread spectrum as applied to distance measurement are covered in Chapter 5 and Chapter 11, respectively. A system is spread spectrum if it has the following properties [1]:
The signal's bandwidth is significantly greater than the minimum necessary to pass the data or symbol rate.
The spreading signal that causes the increased bandwidth is independent of the data.
Despreading the signal at the receiver is done by synchronizing and correlating a locally created replica of the spreading signal.
The main advantages of using spread spectrum techniques, compared to narrowband, are:
Reduced spectrum power density for a given transmitted power.
Increased immunity to jamming and cochannel interference.
Reduced interference to other cochannel signals.
Allows code division multiple access for concurrent use of channel by multiple terminals using the same carrier frequency.
An additional benefit of spread spectrum, which is the interest of this book, is the possibility of determining time of arrival...
