Concentric Cell 1 Overview With the development of network, the number of subscribers is on the increase, and the contradiction between insufficient frequency resources and great demand becomes more and more prominent.To improve the system capacity, the dense frequ frequenc ency y reuse reuse techn technolo ology gy should should be used used so as to improv improve e the spectru spectrum m efficiency. However, the dense frequency reuse will increase radio interference considera considerably bly and will possibly possibly exert exert great great influence influence upon the communication communication quality. Therefore, in the dense frequency reuse pattern, the key problem to solve is how to avoid or reduce the radio interference so as to guarantee the voice quality. The Concentric technology divides ordinary cells into two service layer: big subc subcel elll and and smal smalll subc subcel ell. l. For For mobi mobile le phon phones es with within in the big big subc subcell ell,, the the frequencies of sparse frequency reuse will be preferably allocated (such as BCCH frequency), while for mobiles within the small subcell, the frequencies with dense frequ frequenc ency y resue resue will be alloca allocated ted as much much as possib possible le (such (such as non-BC non-BCCH CH frequencies). The system capacity can be efficiently improved by the dense reuse pattern of frequencies within the small subcell. As shown in the following figure, the mobile phone within the small subcell is quite far from the interference source, so although the dense reuse frequency is used, the voice quality can still be guaranteed. For the mobile phone within the big subcell, since the sparse reuse frequency is used, the voice quality can also be guaranteed.
Cell B
Cell A Signal
Overlaid subcell
Interference
Underlaid subcell
Figure 1 Schematic diagram of dense frequency resue for Concentric Cell If the overlaid subcell is overlaid with the underlaid subcell or overlaid subcell of another cell, then the MS in the overlaid subcell can be directly handed over to the other other cell. cell. Thus, Thus, the conges congestion tion of the underl underlaid aid subcel subcelll can be effici efficien ently tly mitigated. The Concentric technology has divided the cell coverage area into the overlaid subcell and underlaid subcell so that different frequency reuse pattern can be used for TRXs TRXs of the overla overlaid id and underl underlaid aid subcel subcells ls respec respective tively ly.. For For an overla overlaid id subcell, due to its small coverage, the dense frequency reuse pattern can be used, such as the 1*3 frequency reused Pattern. The sparse frequency reuse pattern
can be adopted for the underlaid subcell, such as the reuse pattern of 4*3. Due to the factors listed above, the Concentric technology, with tightly frequency reused pattern adopted for the overlaid subcell, can provide more network capacity than the MRP do. while guaranteeing the network quality. For example, suppose the underlaid subcell is only configured with one TRX (BCCH), and the 4*3 frequency reuse pattern is adopted. If all the other TCH TRXs are configured within the overlaid subcell with the 1*3 frequency reuse pattern, the Concentric Cell would be completely the same as the 1*3 cell, and the average frequency reuse degree would also be the same as that of the 1*3 reuse pattern. In this condition, the Concentric can efficiently reduce the interference upon the whole netwowrk and obtain better network quality than 1*3 without reducing the network capacity. By employing BCCH with high power amplifier,, the coverage of cell can be widened. However, the actual power provided by the BCCH TRX is greater than that provided by other TRXs, therefore, different TRXs will have different coverage distances. When configuring large base station, such as station type S6/6/6, since the Huawei antenna &feeder system uses the combining mode of CDU and SCU (or the mode of EDU+CDU as will be used in the future), combiners of different TRXs may have different losses. Thus, different TRX antenna feeder interfaces in the same cell will provide different powers, which leads to different coverage distances physically. However, the cell coverage is determined by the TRX with small coverage, so the cell coverage is greatly limited. With the application of the Concentric technology, the TRX with wide coverage can serve as the big subcell of the Concentric and the TRX with small coverage can serve as the small subcell so as to ensure the capacity at the near end of the site. Thuse, the cell radius is increased.
Overlaid subcell Underlaid subcell
Figure 2 Schematic diagram of wide Concentric Cell coverage The following table indicates the increased cell coverage area after the application of Concentric Cell in typical station type, The data is a theoretic one which is based on the analysis of the loss for different combining mode: Number
Combining mode
Low-loss TRX
High-loss TRX
Coverage
loss
loss
area
of TRXs in the
increased
cell
after the applicatio n of Concentri c Cell
3
CDU + CDU
1.0dB
4.5dB
27%
4, 5
CDU + CDU + SCU
1.0dB
8.0dB
60%
4, 5
CDU + CDU + CDU
1.0dB
4.5dB
27%
5, 6
CDU + CDU + SCU
4.5dB
8.0dB
27%
Table 1 Change of coverage after the application of Concentric Cell in typical station type
2 System Architecture The Concentric Cell function mainly involves the radio resource management module and the handover decision, which is integrated with the existing radio resource management and handover decision functions of the modules. The background data controls whether the Concentric Cell function will be used and at the same time controls relevant operational parameters. Duirng the call setup, the Concentric Cell channel allocation controls the allocation of radio channels of appropriate Concentric layer (overlaid subcell or underlaid subcell) to different calls and the handover decision controls the handover of calls between the overlaid and underlaid subcells. Thus, it is guaranteed that the appropriate Concentric layer will provide appropriate services all along during the call process. O MC
MSC
DB
OS
Channel Allocation of UO cell RR
AIR
BTSM
RRM ABIS
BSSOMAP BSC
LAPD
UnderlayOverlay HO
BTS
Figure 3 The position of Concentric Cell in the BSC software system
3 System Function 3.1 Interface Function of Concentric Cell From the background, the user can control whether the Concentric Cell function will be used and can configure relevant parameters. Also the traffic index after the
Concentric is in service can be obtained to guide the adjustment of network optimization parameters.
3.2 Technical Characteristics of Concentric Cell The division of Huawei Concentric Cell into overlaid and underlaid subcells is based upon the downlink receiving level and timing advance of mobile phones (as shown in the following figure). Both the receiving level threshold and the timing advance threshold can be configured in the background. Therefore, the borders of the overlaid and underlaid subcells can be adjusted flexibly so that the overlaid and underlaid subcells can share the traffic reasonably under the precondition of network performance.
Figure 4 Division of Concentric Cell into overlaid and underlaid subcells
3.2.1 Channel Allocation Technology for Concentric Cell The channel allocation technology for Concentric Cell means that different allocation policies are used in different channel allocation conditions with full consideration of the characteristics of the Concentric Cell, which mainly includes the following conditions: 1. Instant assignment Without receiving level and TA for reference when the instant assignment is carried out, . the SDCCH channel on the underlaid subcell will be allocated preferably to guarantee the QoS,. Only when there is no available signaling channel on the underlaid subcell will the signaling channels on the overlaid subcell be allocated. 2. Assignment The Concentric channel allocation policy is used. When in the overlaid subcell, a subscriber should be allocated with the overlaid subcell channel, or with underlaid subcell channel only when overlaid subcell channels is not available.. Similarly, when in the underlaid subcell, a subscriber should be allocated with the underlaid subcell channel, or with the overlaid subcell channel only when there is no available underlaid subcell channel. Thus the appropriate service layer will provide the subscriber with quality service. 3. Intra-BSC Handover
It is applicable to non-Concentric handover and direct handover of overlaid subcell to the neighboring cell. The intra-BSC handover adopts the Concentric channel allocation policy so that t he appropriate service layer will provide service for mobile phones handed over. 4. Inter-BSC Handover Since the receiving level and TA of the neighboring cell cannot be obtained, the inter-BSC handover selects the following modes through switch: preferably selecting the underlaid subcell, preferably selecting the overlaid subcell, or without policy.
3.2.2 Concentric Cell Handover Technology The Concentric handover decision technology expands Huawei handover algorithm so that the BSC can guide the traffic intelligently for the reasonable utilization of the frequency resources. Based upon the existing handover algorithm, the Concentric Cell handover technology has been added with the Concentric handover decision function to implement the ordinary Concentric technology. When a mobile phone is crossing the border of the underlaid and ovrlaid subcells, the Concentric handover can be initi ated so that the mobile phone can set up call connection in an appropriate service layer. Yet if the handover target layer is congested, the handover will not be initiated. For example: a handover from the Overlaid subcell to the Underlaid subcell needs to be initiated according to the handover decision. If upon checking it is found that there is no idle channel for assignment in the Underlaid subcell, then the handover will not be initiated.
4 Technical Parameters Please refer to the following table for the data configurations and descriptions related to Concentric Cell: Data table
Data item
Meaning
Value
Suggestions
Can
range and
on value
dynamic
unit
selection
setting be made, command word
Handover/IC HO
U/O Signal
data table
intensity difference
The difference of 0 to 63(dB)
Power
It can be
powers between
difference
dynamicall
the overlaid and
between
y set. The
underlaid
overlaid and
command
subcells and the
underlaid
word is
difference of
amplifiers +
“Configure
path losses
Difference
handover
between them
between
data” and
cause different
combiner
the
signal strength
insersion
parameter
mobile phones
losses +
is the cell
receive. The
Difference
ID.
parameter
between path
indicates the
losses caused
value for
by different
compensating
antennas +
the powers of
Difference
the overlaid and
between path
underlaid
losses caused
subcells.
by different frequency selectivities: Please read the value onsite and select multiple measurement points if the overlaid and underlaid subcells use different antennas.
Rx level threshold
Rx level hysteresis
The receiving
0 to 63
≥ Edge
It can be
(dBm)
handover
dynamicall
the receiving
threshold +
y set. The
level hysteresis,
Signal
command
TA threshold and
strength
word
TA hysteresis
difference
is“Configur
work together to
between
e handover
determine the
overlaid and
data” and
area of the
underlaid
the
overlaid and
subcells
parameter
level threshold,
underlaid
is the cell
subcells.
ID
The
It can be
0 to
dynamica
hysteresis, the
level threshold
lly set.
receiving level
- Edge
threshold, TA
handover
command
threshold and
threshold
word is
receivinglevel
TA hysteresis
63(dBm)
The
“Configur
work together to
e
determine the
handover
area of the
data” and
overlaid and
the
underlaid
paramete
subcells
r is the cell ID
TA threshold
Please give
It can be
threshold,
the explicit
dynamica
Receiving level
geographic
lly set.
threshold,
division of
Receiving level
the overlaid
command
hysteresis and
and underlaid
word is
subcells,
“Configur
work together to
which can
e
determine the
assist to
handover
area of the
help adjst the
data” and
overlaid and
traffic and
the
underlaid
coverage of
paramete
subcells
the overlaid
r is the
and underlaid
cell ID
The TA
0 to 63
TA hysteresis
The
subcells. TA hysteresis
The TA
0 to 63
0
It can be
hysteresis, the
dynamicall
receiving level
y set. The
threshold,
command
Receiving level
word is
hysteresis and
“Configure
TA threshold
handover
work together to
data” and
determine the
the
area of the
parameter
overlaid and
is the cell
underlaid
ID
subcells
IC HO
This parameter
0 to 16 (Second)
5
It can be
measurem
and the
ent time
Concentric
y set. The
handover
command
duration work
word is
together to
“Configure
controls the
handover
Concentric
data” and
handover
the
frequency
parameter
dynamicall
is the cell
ID
IC HO duration
This parameter and statistic
0 to 16
4
(Second)
It can be dynamicall
time of
y set. The
Concentric
command
handover work
word
together to
is“Configur
controls the
e handover
Concentric
data” and
handover
the
frequency.
parameter is the cell ID
Assign
There are the
System
System
It can be
optimization
dynamica
optimum
following TCH
optimization,
layer
assignment
underlaid
modes in
subcell,
Concentric Cell:
overlaid
command
(1) According to
subcell, not
word is
the SDCCH
selected
“Configur
measurement
preferably
e
lly set. The
report, the
handover
system
data” and
determines the
the
service layer to
paramete
be preferably
r is the
assigned; (2)
cell ID
The underlaid subcell is preferably selected for TCH assignment; (3) The overlaid subcell is preferably selected for the assignment; (4) No special processing will be conducted. Assign-
First select the
0 to
If the SDCCH is
It can be
optimun-
preferable layer
63(dBm)
in the
dynamicall
level
in assignment
underlaid
y set. The
threshold
as the “System
subcell, Edge
command
optimization” .
handover
word is
By estimating
threshold +
“Configure
(interpolate and
Signal
handover
filter) the
strength
data” and
current SDCCH
difference
the
level value
between
parameter
according to the
overlaid and
is the cell
uplink
underlaid
ID
measurement
subcells +
value in the
Uplink/downlin
SDCCH
k balance
Measurement
tolerance +
Report, and
Difference
comparing it
tolerance
with the
between
“Preferably
SDCCH and
selected level
TCH; If the
threshold in
SDCCH is in
assignment”
the overlaid
can the
subcell, then
underlaid or
Edge handover
overlaid channel
threshold +
be assigned.
Uplink/downlin k balance tolerance + Difference tolerance between SDCCH and TCH
IntraBSC
There are two
Yes, No
Yes
It can be
inc-cell HO
processing
dynamicall
pref. alg.
methods for
y set. The
incoming cell
command
handover
word is
request within
“Configure
the BSC if a cell
handover
is configured as
data” and
the Concentric
the
Cell: (1) No
parameter
special
is the cell
processing will
ID
be conducted for channel allocation; (2) Add the BCCH measurement value of the destination cell to the inter-cell handover request within the BSC, so as to provide basis for Concentric to determine and compare the receiving level threshold without considering the receiving level hysteresis and to select preferably assigned service layer. Incoming-
Determine the
Underlaid
In ordinary
It can be
to-BSC HO
layer where the
subcell,
networking
dynamica
optimum
channel
overlaid
mode, the
lly set.
layer
preferably
subcell,
inter-BSC
selected for
none
handovers are
command
incoming
triggered at
word is
handover is
cell edges. In
“Configur
located.
this case, the
e
underlaid
handover
subcell
data” and
channel can
the
be preferably
paramete
selected; while
r is the
in dual-
cell ID
frequency networking mode, in most cases, the 900/1800
The
systems share the same stations. In this case, there are large numbers of incoming handovers which generally are not triggered at cell edges. Therefore, the overlaid subcell channel can be preferably selected. Handover/Penalty
IC HO
After an
0 to 16
10
It can be
data table
failure
Concentric
(Second)
penalty
handover failure
y set. The
duration
(regardless of
command
handover from
word
the big subcell
is“Configur
to the small
e handover
subcell or from
data” and
the small subcell
the
to the big
parameter
subcell), during
is the cell
a certain period
ID
dynamicall
of time (setting value of the parameter) the Concentric handover of the call is disabled. Handover/Cell description data table
Cell type
Is it a Concentric
Normal cell,
Configure
It can be
Cell
Concentric
according to
dynamicall
Cell
the actual
y set. The
situations
command word is “Configure handover
data” and the parameter is the cell ID Site/TRX
IC property
configuration table
TRX attributes of Overlaid
If it is an
It can be
Concentric Cell
subcell,
Concentric
dynamicall
underlaid
Cell, configure
y set and
subcell,
it as an
the
none
underlaid
command
subcell or
word is
overlaid
configured
subcell
as
according to
“Configure
the actual situations; if not, configure it as “None”.
TRX attributes”. The parameters include the cell ID and the TRX ID.
Table 2 Relevant data configuration and description of Concentric Cell The parameter configuration of Concentric Cell demands the network planning personnel to configure relevant parameters reasonably, or the network index will be affected.
