PERFORMANCE & IMPLEMENTATION OF
DFH IN LIMITED BANDWIDTH
--Zoran Kostic & Nelson Sollenberger
S. GANGADHAR REDDY
TO BE DISCUSSED:
Comparisons of frequency hops
DFH (Dynamic Frequency Hopping)
Requirements for DFH
DFH implementation via NARA
Fixed channel assignment
Random frequency hopping
frequency diversity is achieved.
Dynamic frequency hopping
combination of dynamic channel
assignment, traditional frequency hopping
& interference avoidance techniques.
WHY TO USE DFH?
System operators may initially deploy
EDGE in small portions of bandwidth
To deploy an all IP network
infrastructure & to avoid interference
he can use this.
Slip over of frequency from other BS
rapid signal quality, path loss
how these are made?
each mobile continuously measures the
quality of all channels available in the system
Measurements are communicated over air to
the base station
Base station periodically updates frequency
hop patterns to optimize overall performance
BS sends info to MS about frequency hop.
SIMILAR PROCESS RUNS IN THE UPLINK
significant signaling overhead
how to reduce
System might restrict hopping pattern to
change only one hop at a time.
System might predefine a set of hopping
patterns and restrict changes to one of those
Synchronization b/t BS is required ?
to ensure different frequency use
DFH IMPLEMENTATION VIA N/W –
ASSISTED RESOURCE ALLOCATION
The signaling overhead required to
communicate the measurement results
to base are reduced by NARA.
It takes the advantage of frame
synchronization on system level &
provides functionality identical to that of
measurement based DFH.
BS monitors user performance & is
reassigned another resource if it
degrades below a threshold.
Signaling over air
Inter base signaling
it is observed that extra signaling
bandwidth to the bandwidth is around
A STAGGERED-FRAME resource management
can be used to avoid the problem of 2 near by BS
simultaneously choosing same resource.
Base stations are frame and super frame
Control reuse pattern is defined in time, according
to which only one base station is allowed to
change frequency hop patterns for the duration of
All base stations get an opportunity to modify
frequency hop patterns of their mobiles once per
The primary goal of the simulation study is to
establish relative performance improvements of
dynamic frequency hopping when compared to
random frequency hopping and fixed channel
The simulation is done on the basis of cumulative
distribution functions(CDFs) indicating the
achievable word error rates ( WERs) as a function of
channel condition,loading, total no. of frequencies
and other factors. 10
A. Comparison of Channel Assignment Techniques
for Fixed Performance Point:
One curve shows the performance of a 12-carrier
system that uses fixed channel allocation for three users
per base station.
Another curve illustrates the performance of
random frequency hopping for four users per base station
(loading of 33%).
A system using dynamic frequency hopping can
serve as many as six users per base station(50% loading) .
Fig. 1. FH versus fixed channel assignment 12
B. Effects of Voice Activity:
The implementation of discontinuous transmission
(DTX) to exploit voice activity results in direct
interference reduction, and thereby in capacity
The capacity of the DFH system for satisfactory
performance falls from six to four users, while the
capacity of the fixed assignment system falls from three
to two. In both cases, DFH offers 100% improvement in
Fig. 2. Voice activity effects 14
C. Uplink Performance Versus Downlink Performance
Two of the main factors that contribute to the
performance difference between the downlink and uplink
1)Different geographical distribution and mobility of
2) Presence of receiver antenna diversity on the uplink.
Strong base station interferers will be easy to avoid by
means of DFH, and thereby improve the performance on
the downlink. On the other hand, the antenna diversity
helps the uplink performance.
Fig. 3. Comparative performance of uplink and downlink for DFH as a
function of occupancy for uncorrelated Rayleigh fading 16
DFH brings about 100% increase in capacity over
fixed channel allocation and 50% increase in capacity
over random frequency hopping.
Although the performance of various systems is
sensitive to the number of available carriers, voice
activity, and channel coherence bandwidth, the system
using DFH offers the greatest overall robustness.
DFH performs equally well for uplink and downlink.
R.L.Pickholtz et al.,”Theory of Spread Spectrum
Communications-A tutorial,”—May 1982
X.Wang and Z.Kostic,”Analysis of frequency-hopped
cellular systems with dynamic FH pattern
“Performance and Implementation of Dynamic
frequency hopping in limited bandwidth cellular
systems,” Zoran Kostic & Nelson Sollenberger, jan
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