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Radio Resource Allocation in UL prezentation
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Abstract;
Introduction;
The radio resource allocation algorithms:
◦ Fair Allocation scheme;
◦ Proportional Allocation scheme.
Simulator description;
Simulation results;
Conclusion;
References.
In this paper is proposed an algorithm which distributes
the available bandwidth proportionally to the channel
conditions while meeting the SINR target by means of
power control.
The results show that the proposed algorithm, when
combined with slow power control, is able to improve
the average cell throughput by approximately 23% with
almost no reduction of the 5% outage average user
throughput.
In the E-UTRAN system the users of the same cell are
orthogonal with each other thus the only interference
present is from other cells.
In this paper, which is intended to be an initial
evaluation of the system performance of E-UTRAN,
the MCS is assumed to be fixed, thus the focus is on
the performance of ATB.
This algorithm equally distributes the available PRBs among the users in the cell. The number of allocated PRBs per UE changes only when the number of UEs in the cell changes because of a handover. The closed loop PC adjusts the transmit power of the UE, in a fast or slow basis, depending on the received SINR in order to match the SINR target. If the received SINR at the Base Station (BS) is less than the SINR target, a power-up command of 1 dB is given to the UE while if the received SINR is greater than the SINR target, a power-down command of 1 dB is given.
This algorithm dynamically adapts the user’s bandwidth to the changing channel condition while trying to match the SINR target by means of either SPC or FPC.
After an initialization phase, in which each UE receives an equal number of PRBs,
the SINR is measured and its ratio to the SINR target is calculated. Using such a
ratio between measured SINR and SINR target, and the number of previously
allocated PRBs, the number of PRBs necessary to match the SINR target while
transmitting at lowest power is calculated.
Similarly, the number of PRBs
necessary to match the SINR
target while transmitting at
highest power is calculated.
These minimum and maximum
numbers of requested PRBs
carry information on the current
channel conditions the UE is
experiencing within the
allocated PRBs.
To begin with, the packet scheduler tries to guarantee the minimum requested
allocation of PRBs to each user. In case the number of available PRBs is less than
the requested number, the allocation will take place in proportion to the minimum
request from each user. If the number of available PRBs is higher than the
minimum requested, the extra PRBs will be distributed among the users
proportionally to the highest request from each of them.
Finally, once the allocation is performed, the power is scaled according to the ratio
between current and previous bandwidth in order to keep power spectral density
constant. Also in this scheme the closed loop PC adjusts the transmit power of the
UE in order to match the SINR target. The aim of this radio allocation scheme is to
allocate more PRBs to users in the BS vicinity which have a lower power spectral
density, than the ones at the cell boundary which have a higher power spectral
density.
This results in a reduction of intercell
interference and consequently in increased
system capacity. The underlying assumption
is that the channel, on a steady-state, will
have a similar behavior over consecutive
PRBs.
ELIISE - Efficient Layer II Simulator
for E-UTRAN, is a multi-cell, multi-
user, dynamic system level simulator to
study advanced RRM in uplink. The
functionalities include channel model,
mobility, handover, Automatic Repeat-
reQuest (ARQ), PC and ATB.
The simulated network layout assumes
a hexagonal grid with 8 BSs and 3
sectors per BS with a corner-excited
structure.
This figure shows the distribution of the uplink SINR per TTI for all
the UEs in the system. The FA algorithm shows a better matching of
the SINR target than the PA algorithm because the allocation of the
same PRBs to the same UEs over subsequent TTIs makes it easier to
track the fading channel and the more stable intercell interference.
As expected FPC offers
better matching properties
than SPC for both schemes.
pdf of the instantaneous SINR for all UEs measured on a TTI basis
This figure shows that all
UEs have higher time
average SINR when using
PA as compared to FA for
both SPC and FPC. In the
PA case the UEs at the
cell edge receive less
PRBs thus it is easier for
them to reach the SINR
target.
CDF of the time average SINR per UE
The distribution of the
average UE throughput is
shown in this figure. Here
it can be seen how the PA
algorithm trades a small
loss in the lower end of
the throughput range for a
significant improvement
in the higher range.
CDF of the time average throughput per UE
The distribution of the
average number of PRBs
per UE, given in this
figure, shows that the PA
mechanism is a channel
aware scheme, thus it is
able to adapt to the
channel conditions as
shown by the greater
variability in the number
of allocated PRBs. CDF of the time average PRBs per UE
The cell throughput results are shown in this figure. The cell throughput of the
PA scheme is higher than the FA scheme by 23% for the case of slow PC and
15% for the case of fast PC. At 5% outage of the average user throughput the
PA scheme shows a loss of approximately 2% in case of slow PC and a gain of
approximately 18% in case of fast PC. Thus the fairness for the users in the
lowest throughput range is preserved.
A possible improvement for the
Quality of Service (QoS) of those
users could be obtained by setting a
minimum requirement on the bit rate.
It is interesting to notice that the gain
from FPC decreases from 22% to
15% when moving from FA to PA.
Average cell throughput and 5% outage average user throughput
On the left, it is clear
that FPC is not able
anymore to guarantee
a SINR matching
better than SPC. On
the right, the gain of
FPC is reduced to
7% for the case of
FA.
pdf of the instantaneous SINR for all UEs (measured on a TTI basis)
and average cell throughput for the case of randomized PRBs
allocation
In this paper have been presented studied the performance of two resource allocation algorithms in combination with SPC and FPC for UTRAN LTE, assuming fixed MCS and SINR target. The results obtained show that the PA algorithm increases the average cell throughput by 23% for the SPC case, while slightly reducing the throughput of the UE in disadvantaged channel conditions.
It is shown to depend on the allocation scheme and it decreases from 22% to 15% for PA because of higher interference variations.
Future studies will concern the integration and performance evaluation of other LA functionalities.
[1] 3GPP TR 25.814 V7.0.0 (2006-06), “Physical Layer Aspects for Evolved UTRA”.
[2] A. Toskala and P.E. Mogensen, “UTRAN long term evolution in 3GPP”, International Symposium on Wireless Personal Multimedia Communications, 2005.
[3] A. Toskala, H. Holma, K. Pajukoski and E. Tiirola, “UTRAN long term evolution in 3GPP”, IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Sep. 2006.
[4] A. Pokhariyal, T.E. Kolding and P.E. Mogensen, “Performance of Downlink Frequency Domain Packet Scheduling for the UTRAN Long Term Evolution”, IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Sep. 2006
[5] J. Lim, H.G. Myung, K. Oh and D.J. Goodman, “Channel-Dependent Scheduling of Uplink Single Carrier FDMA Systems”. IEEE Vehicular Technology Conference, Sep. 2006
[6] H. Holma and A. Toskala, Eds., “WCDMA for UMTS”, 3rd ed., John Wiley & Sons.
[7] T. Hyt¨onen, “Optimal wrap-around network simulation”, Helsinki University of Technology Report, A432, 2001.
[8] 3GPP TR 25.943, “Deployment aspects”.
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