2. 2
Muhieddin Najib - Jan. 12, 2000 - Pag 2
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Assuming a Multicarrier Environment
• Without Pooling Resources:
— Using basic IS-95 A/B steering
mechanisms (Hashing, Global Service
Redirection) , mobiles are monitoring a
paging channel in a specific frequency.
Individual Mobiles will always go to a
specific carrier.
— Resources between carriers are not
shared.
— Trunking is restricted to be within a
single carrier.
Underlying
frequency
Overlaid
frequency
f2
f1
Voice
Resources
Available
Voice
Resources
Available
• What MCTA does:
— Balances traffic at call origination
/termination, allocating calls through the
carriers assigned in a multicarrier cell
site.
— Power Amplifier resources are pooled.
— Trunking is now achieved across
multiple carriers.
f2
f1 Resources Available
for origination / termination
across the carriers.
f1
f2 Resources Available for
origination / termination
across the carriers.
3. 3
Muhieddin Najib - Jan. 12, 2000 - Pag 3
Nortel Networks Confidential
Without MCTA With MCTA
Baseline Scenario:
• Erl (2 carriers) = 2* Erl (1 carrier)
• Erl (3 carriers) = 3* Erl (1 carrier)
• Hashing and GSR steering mechanisms can
balance mobiles between carriers in idle mode, but
mobiles in traffic state can still be unbalanced.
• Second carrier under - utilized; f1 starts blocking.
• Non optimal use of resources; Erlang capacity not
fully maximized.
MCTA Capacity Benefits (depending
on vocoder, GOS, number of carriers):
• Resources Pooling:
7% - 16% Increase
Defer the need for additional Carriers
• f1 / f2 have more uniform usage.
• Amplifier Power is more efficiently used.
• Blocking is reduced.
• Aggregated Erlang capacity increases.
f 1
f 2
f 1
f 2
Resources only from f2
Resources only from f1
Resources across f1-f2
Why MCTA?
Resources across f1-f2
Intra-Carrier Interference
4. 4
Muhieddin Najib - Jan. 12, 2000 - Pag 4
Nortel Networks Confidential
Where is the extra capacity
coming from?
• Think of extra capacity as coming from “Power
trunking”, not voice channel trunking.
— Capacity is typically dominated by the available Forward Link
Power*, not voice channel (channel elements, vocoders)
resources.
— MCTA gives mobiles the choice of accessing different carriers
based on available forward link power.
• Increased carried traffic comes from statistical
efficiencies of better access for users to available
traffic channel power.
*The Forward Link Power versus the interference level is balanced to maintain a nominal Eb/No,
therefore just increasing Power Amplifier output is not enough to increase capacity
5. 5
Muhieddin Najib - Jan. 12, 2000 - Pag 5
Nortel Networks Confidential
How Does MCTA Reduce RF Blocking?
Consider the following series of RF Events …...
O O O T O O O T RF Event (time)
HPA
Power
on
F
1
O: Origination
T: Termination
X: Call Blocked
•To simplify
analysis, we
assume that all
channels remain
static during RF
Events.
•Both Blocks are
gone away
•HPA power
fluctuation is
reduced
•Average HPA
power is reduced
Max HPA Power Blocking Threshold
X X
GSR/
Hashing
O O O T O O O T RF Event (time)
HPA
Power
on
F
1
MCTA
These calls are allocated
to F2 by MCTA
6. 6
Muhieddin Najib - Jan. 12, 2000 - Pag 6
Nortel Networks Confidential
How Does Reducing HPA Power
Fluctuations Translate into Capacity Gain?
Max. HPA
Power
HPA Moving
Average
GSR/Hashing MCTA
• If average loading is the same, then RF blocking is reduced since power
fluctuations on HPA are reduced.
• If RF blocking is the same, then average loading (i.e., Erlangs) can be
increased when MCTA is used.
Blocking Region
Blocking Region
Call Blocking
Threshold
Time Time
7. 7
Muhieddin Najib - Jan. 12, 2000 - Pag 7
Nortel Networks Confidential
Same RF Blocking Performance with and
without MCTA
Average Loading
with MCTA
Average Loading
without MCTA
• If blocking is kept the same, the difference in average loading with
and without represents the MCTA Erlang capacity gain.
8. 8
Muhieddin Najib - Jan. 12, 2000 - Pag 8
Nortel Networks Confidential
MCTA Improvement Factors over Perfect
Pooling Gain for 1% GOS, 13k vocoder:
• Percentage increase can be quoted as versus perfect pooling or as net gain
(% increase over offered Erlangs without MCTA)
• If perfect pooling (trunking) was realized, then increase in offered Erlangs over
no pooling would be:
— 2-Carrier Perfect Pool: Erlang improvement = 28%across all carries.
Total Erlang capacity of both carriers = 2*(1 + 0.28) = 2.56 times the Erlang
capacity of a single carrier.
— 3-Carrier Perfect Pool: Erlang improvement = 42% across all carriers.
Total Erlang capacity of the three carriers = 3*(1 + 0.42) = 4.26 times the Erlang
capacity of a single carrier.
• MCTA gain versus perfect pooling:
— 2-carrier MCTA: 43% of perfect pooling gain
— 3-carrier MCTA: 38% of perfect pooling gain
• Thus, the MCTA Net gain
— 2-carrier MCTA: (0.28)(0.43)(100) = 12% net gain across each carrier.
Total Erlang capacity of both carriers = 2*(1 + 0.12) = 2.24 times the Erlang
capacity of a single carrier.
— 3-carrier MCTA: (0.42)(0.38)(100) = 16% net gain across each carrier.
Total Erlang capacity of the three carriers = 3*(1 + 0.16) = 3.48 times the Erlang
capacity of a single carrier.
9. 9
Muhieddin Najib - Jan. 12, 2000 - Pag 9
Nortel Networks Confidential
Example:
MCTA Erlang Capacity (per sector) for 1%
GOS, 13k Vocoder:
• 1st carrier - 13 users/sector, 6.61 Erlangs
• 2nd carrier - (6.61 Erlangs)(2.24) = 14.81 Erlangs*
• 3rd carrier - (6.61 Erlangs)(3.48) = 23.00 Erlangs*
* Note: These results are from simulations only! Field testing
is required for validation of results.
10. 10
Muhieddin Najib - Jan. 12, 2000 - Pag 10
Nortel Networks Confidential
Why not Achieving Perfect Pooling Gain?
• MCTA allows for an increase in average loading (i.e.,
Erlangs) if the same blocking performance is maintained.
• In CDMA, as average loading increases, the average intra-
carrier interference also increases.
—Consequently, the power per user (PPU) also needs to be increased
to maintain the same system performance (FER and Dropped calls).
• The increase in PPU limits the MCTA capacity performance
since RF capacity is inversely proportional to PPU.
• Perfect pooling assumes that efficient utilization of CDMA
channels will not penalized system RF performance.
—Thus, Erlang-B formula may not always hold in CDMA systems.
• If RF performance need not be the same before and after
MCTA, it is possible that the MCTA gain comes close to
perfect pooling gain.
—This requires changes to the datafills that affect Eb/No, FER and
Dropped calls.
