B3P2 Flashcards
What is channel bonding
in which two or more channels are used together
What is FDD frequency division duplexing
the use of separate frequency bands enabling simultaneous uplink and downlink communication
What is TDD time division duplexing
uplink and downlink share same frequency but access to frequency rapidly alternates between uplink and downlink
What is Wideband code division multiple access WCDMA
The multiple-access method used in the radio networks of third-generation mobile communications. It exploits the orthogonality of certain families of chip sequence (referred to as codes). Encoding data with a chip sequence renders it orthogonal to data encoded with a different sequence, enabling separate data streams to be transmitted simultaneously over a channel. Encoding with a chip sequence also gives the benefits of spectrum spreading and processing gain.
What are the 2 main sorts of code in WCDMA
channelization codes and scrambling codes
What is a channelisation code
define channels for data
What is a scrambling code
Applied to channelization encoded signals to give them a noise like character
How do chanelisation codes work
Channelisation encoding in WCDMA consists of replacing each of the 1s and 0s of a users binary data stream with several shorter duration chips prior to transmission
Channelisation codes must be orthogonal, the correlation of one channelization code with another channelization code must result in 0
What are walsh codes
not restricted to 4 chips but number of chips is always an integer power of 2
How to scrambling codes work
Also called pseudo-random codes or pseudo noise codes
Applied to channelization encoded data to give noise like properties
Prevent interference from neighbouring base stations what belong to same operator operating at same frequency
Base stations can be distinguished from each other by their scrambling codes
Power control – the base station instructs the devices how powerful a signal to transmit
What is Quadrature transmission and bit rates in WCDMA
In the downlink, quadrature phase shift keying effectively doubles the data rate because it gives two orthogonal data paths that are used simultaneously, the I phase and Q phase
What are the problems of WCDMA
The relationship between chip rate, data and channel width
Another problem with WCDMA is power control. Power control of mobile devices by the base station ensures that signals from devices arrive at the base station with approx. equal power so that signals from devices close to the base station do not swamp those further away
What is Orthogonal frequency division multiple access OFDMA
OFDMA is the access method for LTE downlink
What is OFDM
OFDM is at the most basic level, a form of FDM
OFDM is described as a technique for multicarrier modulation
What are subcarriers
In OFDM, one of the set of carrier waves that together comprise the OFDM signal.
