Improving Grade of Service GOS While Reducing RF Channels Wireless service providers are adopting new deployment strategies to reduce network costs and improve quality of service.. In on
Trang 1New Network Architecture
Network Costs and Improve Quality of Service
Trang 2Improving Grade of Service (GOS) While Reducing RF Channels
Wireless service providers are adopting new deployment strategies
to reduce network costs and improve quality of service In one urban market, a major national wireless service provider has improved network traffic loading and significantly boosted network
RF performance by centralizing radio equipment and deploying digital RF transport technology The digital RF transport systems operate in simulcast mode and reproduce the signal at radiating points throughout the network The new network architecture has produced trunking and channel re-use performance gains that enable the service provider to deliver greater GOS while reducing the number of RF channels
To achieve greater capacity with fewer RF channels, network designers used two or more ADC Digivance digital RF transport systems operating in “simulcast” mode at radiating points throughout the network This white paper describes that simulcast network architecture, network traffic loading improvements and how the team determined the number of RF channels needed to achieve the desired GOS
Reduce Network Costs and Improve Quality of Service
New Network Architecture
Trang 3What is "Simulcast"?
A wireless simulcast communications system is defined
as a signal (or group of signals) that is transmitted from
a central transceiver and identically reproduced to
several radiating points, with all received signals from
these radiating points sent for recovery at the central
transceiver’s receive circuitry
In the case of Digivance technology, the “central
transceiver” is the Base Transceiver System
(BTS)/Digivance host location, and the “several radiating
points” are multiple Digivance remote units, as shown
in this example of a Long-Range Coverage Solution
(LRCS) simulcast deployment diagram:
ADC’s patented Digivance digital RF spectrum transport
solution is uniquely suited as the infrastructure of a
simulcast network due to the inherent qualities of a
digital fiber system These benefits include:
• Highest optical budget in the transport industry
• Exceptional RF performance throughout entire
optical budget
• Lowest reverse path cascaded noise figure in the
transport industry
• Present WDM and CWDM optic capability, with
future DWDM capability
How Does a Digivance Simulcast System Create a Network Traffic Loading Improvement?
The benefits of simulcast coverage in the service provider’s urban network are due to a reduction in the number of BTS sectors and an increase in channel loading per sector This improves trunking efficiency (remember:
calls cannot trunk between sectors) In the urban LRCS
network, the new architecture reduced by 30 percent or more of the total number of RF channels required on a multiple link transport system for a specified amount of user grade of service The percentage reduction depended on the number of radiating points and trunks required for the coverage area
In all communications systems that carry more than one user at a time, several communication links (i.e voice
“trunks”) must be provisioned to allow for all anticipated users to gain reasonable access to the network What determines “reasonable access” is the designated “grade of service” (GOS), which is the acceptable amount of network blocking of incoming call attempts Typical wireless network designs in the United States provision channels to provide voice services at a GOS of approximately 2 percent, with data services typically provisioned at a GOS of 4 to 5 percent
To determine the number of RF channels (voice trunks), the GOS and anticipated traffic intensity (Erlangs) must
be known Conversely, if you know the number of voice trunks available and the GOS, you can calculate traffic intensity supported
“Trunking efficiency” is simply the observation that the more voice trunks available - the less the chance of blocking, and is best explained by the Erlang B (non-queuing requests) formula:
Where:
B = Blocking% (GOS)
A = Offered Traffic Load (Erlangs)
N = Number of Available Trunks
BTS
Site
Controller
BTS
Sector
1
Interface Panel
FP 3:1
RP 3:1
Host 1 Host 2 Host 3
BTS
Sector
1
Interface Panel
FP 2:1
RP 2:1
Host 4 Host 5
Remote 1 Remote 2 Remote 3 Remote 4 Remote 5
AN N!
B=
i
i!
i=0
N A
∑
Trang 4Core Urban Market - A “Real World”
Case Study
Here is an actual service provider’s market application of
LRCS in two separate 2:1 simulcast configurations In
the original metro “RF hotel” configuration of five
radiating points (a traditional BTS deployment of one
radiating point per sector), the service provider
operated five BTS sectors dedicated to five separate
radiating points in strategic locations to obtain desired
capacity and coverage in the metro core, as shown in
diagram below:
With average Radio Frequency channel (RFc)
provisioning for this configuration of six RFcs (a
maximum of 17 interconnect voice trunks) per sector,
the acceptable offered interconnect load (GOS = <2%)
was 10.6 Erlangs per sector
Given an interconnect traffic intensity total in Erlangs =
(10.6E * (# of sectors)), any two sectors within this BTS
would support 21.2 Erlangs at 2% GOS
After the five LRCS sectors were optimized and
confirmed to be operating with excellent statistics, the
urban market began to test the ADC recommended
simulcast strategies
This is a diagram detailing the customer conversion to
one sector of simulcast:
By combining two of these radiating points into a single BTS sector and increasing the base radio count of that sector to 10RFcs (26-29 interconnect voice trunks maximum), trunking efficiencies are increased to 21.1 Erlangs at 2% GOS traffic support on a single simulcast sector
Capacity comparison:
(21.1E)/(21.2E) = 0.995%
Required Radio Frequency Channels:
10RFc(simulcast)/12RFc(RFc S 2 sectors) = 0.833%
An initial conclusion can be drawn that this configuration allows for virtually identical capacity (at 0.995%) with 17 percent fewer BTS radio channels required… an impressive number in itself There is also
an opportunity for data services to realize the benefits
of increased trunking efficiencies of a Digivance digital simulcast network
So for the direct connect and packet data services queuing calculation using Erlang C provisioning is:
In this network deployment, the service provider realized significant cost savings and found that they could actually reduce to one sector with nine RFcs from two sectors averaging 13 RFcs (2 sectors of 6RFc + 7 RFc), a BTS radio reduction of 31percent
In addition, it was observed that low cost/low power 2:1 splitters and combiners could be used for forward and reverse paths to couple signals between a single interface and two host units This reduced the amount
of interface circuitry required in the network and produced another cost savings from the simulcast system After realizing this savings (and being assured
by continued excellent system performance statistics and RF measurements) the service provider repeated this 2:1 simulcast process again with the same results
BTS
Site A
Controller
BTS
Site B
Controller
Sector 1
(6RFc)
Sector 2
(6RFc)
Sector 3
(6RFc)
Sector 4
(6RFc)
Sector 5
(6RFc)
BTS Interface BTS Interface BTS Interface
BTS Interface BTS Interface
Host 1 Remote 1 Host 2
Host 3
Host 4 Host 5
Remote 2 Remote 3
Remote 4 Remote 5
BTS
Site A
Controller
Sector 1
Sector 2
Sector 3
BTS Interface BTS Interface BTS Interface
Host 1 Remote 1 Host 2
Host 3
Remote 2 Remote 3
A NN N! (N-A)
i
i!
P(>0)=
A
∑
N-1
+ A NN N! (N-A) i=0
Trang 5Final Configuration:
The estimated equipment savings realized for the
service provider’s three sector simulcast application vs a
five sector application were as follows:
Estimated savings in required BTS and LRCS equipment:
• 7 fewer base radios required (est as provided by
customer) 7* $5,000 = $35,000
• 50% fewer LRCS-BTS Interfaces required (list, 2
primary panels) 2* $2,900 = $5,800
• 30% fewer high power TX combiners required
2* $3,000 = $6,000
• 30% less Rx Multi-coupling
2* $2,000 = $4,000
Estimated expense in required simulcast equipment:
• 4 Low power splitters and combiners and coaxial leads 4* $400 = $1,600
Savings realized by converting four sectors to two simulcasts:
Total Equipment Savings = $49,200 (less expenses) Additional operational savings:
• Reduced BTS space and power requirement (less equipment)
• BTS Ops/Field/Perf/Design Engineering support (fewer RF channels)
BTS
Site A
Controller
BTS
Site B
Controller
Sector 1 (6RFc) Sector 2 (9RFc) Sector 3
Sector 4 (9RFc) Sector 5
BTS Interface BTS Interface BTS Interface
BTS Interface BTS Interface
Host 1 Remote 1
Host 2
Host 3
Host 4
Host 5
Remote 2
Remote 3
Remote 4
Remote 5
Trang 6Additional Benefits of Simulcast
Simulcast networks also can substantially reduce
required switch and handoff processing and further
improve trunking efficiencies within a given coverage
area In addition, assigning simulcasts where there are
sequential busy hours between radiating points (i.e.: a
sports stadium, a mega mall, and a business area may
all have differing busy hours) can also greatly enhance
revenue per base radio due to an increase in duration
of peak minutes of use (MOU)
In this urban market application, the service provider's
simulcasts will require less BTS infrastructure, reducing
base radio and RF interfacing equipment and potentially
reducing required base site controllers and required T1
lines to the switching office as well BTS can consolidate
to central locations It virtually eliminates dropped and
poor-quality calls associated with the “ping pong”
handoffs commonly experienced in urban
environments
Another benefit that impacts the entire network is the
substantial opportunity to greatly reduce
co-channel/pilot pollution interference issues and optimize
re-use by judicious use of simulcast This is particularly
true in the network core where it enables the service
provider to achieve the desired metro core in-building
signal penetration while virtually eliminating
under-utilized urban channel sets This has a tremendous
impact for the service provider by more efficiently using
existing allocated spectrum while improving call quality
with lower co-channel interference throughout the
network (less C/I interference)
Conclusions
Digivance networks configured in simulcast deliver service providers a greater return on investment by creating the optimal traffic management scenario of improved base radio utilization (i.e more Erlangs per base radio) and increasing MOU income per base radio
As service provider channel capacity dictates, larger simulcasts of four or six or even more Digivance links can provide still greater network savings while delivering unprecedented network coverage quality
In conclusion, this service provider’s urban market application of a Digivance digital simulcast network significantly enhanced network coverage and capacity
in an urban core environment The more efficient use
of RF frequency resources allows for future growth in services while reducing the need for an expensive and intrusive network allocation of additional RF bandwidth
Trang 8Web Site: www.adc.com
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