Product Info

System Description WipLL Radio Technology - Physical Layer
25030311-08 Airspan Networks Inc. 2-3
The advantages of implementing FH-CDMA in the WipLL system include the
following:
 Frequency Hopping Spread Spectrum (FHSS) is based on interference
avoidance. Narrow band interference that does not meet the SNR blocks only a
few hops, decreasing the throughput only partially.
 The required spectrum for an FHSS system is flexible in that it does not have to
be contiguous.
 FHSS can coexist with other systems in the same spectrum band.
 To intercept transmission, a receiver must “know” the hopping sequence
therefore, FHSS ensures security.
 Frequency diversity copes with the frequency selective fading and multipath.
The RF channel obtained by the WipLL operator is divided into n 1-MHz sub-
channels, with center frequencies located at integer multiples of 1 MHz (see Figure
2-2). These sub-channels are organized into a set of orthogonal hopping sequences.
Several methodologies are available for creating these sequences, depending on
available spectrum and local regulations.
Sub-channel
RF channel
Assigned band
Figure 2-2: Relationship between “sub-channel”, “RF channel”, and “assigned
channel”