My understanding is that 1 Data Bit, when encoded using Barker 11, is “spread” (encoded) into 11 digits, individually called Chips. And this group of 11 Chips is collectively referred to as a Symbol. But reading through various publications, I’m left confused and not so sure.
For example from Cisco’s WIFUND – Implementing Cisco Wireless Network Fundamentals – Student Guide it states…
“The Barker code allows you to send a chip of 11 digits (or symbols) instead of the value itself…”
While in the book CCNA Wireless 640-722 Official Cert Guide it states…
“Each of the new coded bits is called a chip. The complete group of chips representing a data bit is called a symbol.”
These two statements seem to contradict each other or am I missing something obvious here? The first one states that a Chip contains 11 digits, while the latter seems to state that the individual digits are called Chips and together are called a Symbol.
However, it seems a Symbol can also be associated with Modulation, in particular Phase Modulation i.e. changes in the phase of the carrier wave can represent more than one “bit” of information. But does that bit represent a Data Bit or a Chip? And this is another point of confusion for me.
From CCNA Wireless 640-722 Official Cert Guide
It states in relating to DQPSK “The main difference is that the data bits are taken pairwise (after scrambling), and encoded so that two-bit pairs map to 11-chip symbols”
From the book Scalable VoIP Mobility
It states “This time, chips are taken two at a time and modulated onto the carrier signal by using DQPSK”
So, one book states, in relation to DQPSK modulation that 2 Data Bits are taken and the other that 2 Chips are taken. How can this be?
I know these questions may seem somewhat irrelevant, but it seems understanding Chips and Symbols are fundamental to understanding wireless / RF communications.
