II. Technical description 1) Power control classification
2.2.3 Extended Cell
I. Overview
In GSM specifications, the TA of cell has a restriction of 63 bit at the radio interface, which results that the cell coverage radius should be within 35km. In regions such as
of radius within 35km. Supported by BTS hardware, it can cover a range with radius of 120km under its ideal state. Carriers can use this technology to fast construct their GSM networks with fewer stations and at lower cost, and to attract the mobile subscribers in special regions so as to improve profit.
II. Technical description
When the cell coverage radius exceeds 35km, signal delay will exceed the duration corresponding with the maximum value 63 bit specified in GSM specifications. If an MS reaches the ordinary coverage verge, it will transmit at the maximum TA allowed by system; if the MS continues to move outside of cell range, the system is no longer able to implement adaptive regulation on TA value due to the TA has reached its maximum, and part of signaling transmitted by MS will reach BTS receiver at next time slot. It is this principle that extended cell uses to realize the cell extension, i. e. two continuous time slots in BTS are specified for each MS call, and the receiving window of BTS receiver is also extended to a width of two time slots thus the cell coverage radius is extended to over 35km. In order to enable MSs in extended range to initiate call at any time, two time slots should be always distributed to BCCH, CCCH and SDCCH.
The frame TDMA of GSM radio interface is composed of 8 time slots. Each time slot is a channel. Normally, the system uses TA to make the uplink signals of MSs with different distances reach within the corresponding local time slot. TA supports a maximum of 63 bit. In order to support the extended MS signals over 63 bit, dual time slot solution binds odd and even time slots and regards each TDMA frame as only with four channels: 0/1, 2/3, 4/5, 6/7. . For MS, only channel 0, 2, 4, and 6 are distributed.
The MS in the range 0~35km, its TA value changes within the range 0~63. The TA value of MS with radius over 35km is always maintained as 63. While BTS demodulates uplink data in two continuous time slots. TA value of TA in MS has a maximum of 63+156. 25 = 219. 25 bit. The principle of extended cell delay regulation is as shown in Figure 2-28.
DELAY<=63
After TA adjustment
After TA adjustment TS0
TS0
TS1
TS1
TS2
TS2
unlink data
delay>63
demodulation range
Dual times lot extendend cell
Figure 2-28 Principle of extended cell delay regulation
If all carrier frequencies in a cell are set as ordinary ones, this is called cell level dual time slot solution. If part of carrier frequencies in a cell are set as ordinary ones and other carrier frequencies are configured as dual time slot ones, and BCCH is located in dual time slot carrier, then this is called carrier level dual time slot solution.
When carrier level dual time slot extended cell is adopted, there are ordinary carrier and dual time slot ones. BCCH in dual time slot guarantees the random access of any areas. The calls within TA value accessed randomly being within 35km radius are distributed to ordinary carrier; while the calls within 34~120km radius and the incoming handovers are distributed to dual time slot carrier. For the incoming handovers to be found as 0~35km ones, the system can handover them again to ordinary carrier. When the calling MS crosses 35 km line, this will lead to an intra-cell handover, which is from the dual time slot frequency to the ordinary one or from the ordinary to dual time slot frequency. The conversion of carrier frequencies between ordinary one and dual time slot one can be set through BSC data configuration
III. Parameter
“Cell Extension Type ” in [Cell\Cell Attribute Table]
“CH Type ” in [Local Office\Radio Channel Configuration Table]
“TA Hysteresis ” in [Handover\ Concentric cell Handover Table]
2.2.4 IUO
I. Overview
With the development of GSM network, the number of subscribers increases gradually, so the contradict between short frequency resource and great demand is particularly obvious. In order to increase capacity, the technology of aggressive frequency reuse should be used to improve the frequency utilization. However, the aggressive frequency reuse increases the radio interference greatly and even to affect the communication quality seriously. Under the circumstance of aggressive frequency reuse, the IUO technology can be used to avoid or decrease radio interference so as to guarantee communication quality. The IUO technology divides an ordinary cell into two service layers: OverLaid subcell and UnderLaid subcell. For the MS in the UnderLaid subcell, try to distribute the less reuse frequency, such as BCCH frequency; for the MS in the OverLaid subcell, try to distribute the more reuse frequency, such as frequency except BCCH. The frequency inside the OverLaid subcell adopts aggressive frequency reuse mode, which can improve system capacity effectively.
II. Technical description
IUO refers to the different carrier circle cells formed by different carrier frequencies in a cell with difference on coverage. Logically, OverLaid subcell and UnderLaid subcell can be regarded as two cells because their coverage areas are different, The OverLaid subcell is the main traffic carrier layer because it has many channels. Its function is to absorb the most subscribers within the cell coverage area. UnderLaid subcell solve the problem of coverage and provide service for the areas not covered by overlaid cell. e The technical description of IUO is as shown in Figure 2-29.
Cell A Cell B
UnderLaid subcell
Interference Signal
OverLaid subcell
Figure 2-29 Aggressive Frequency Reuse of IUO cell
As shown above, the IUO divides the cell coverage into OverLaid subcell and UnderLaid subcell. The carrier frequencies of OverLaid subcell and UnderLaid subcell can adopt different multiplexing modes. For the OverLaid subcell cell, it adopts more reuse frequency mode such as 1x3 due to its small coverage. For the UnderLaid subcell cell, it adopts less reuse frequency mode such as 4x3. After the IUO technology is employed, compared with Multiple Reuse Pattern (MRP), it can greatly increase the network capacity and guarantee the network quality because the OverLaid subcell employs of aggressive frequency reuse mode. In some special cases, the UnderLaid subcell is configured with only one carrier BCCH with the multiplexing mode of 4x3 being adopted and the rest TCH carrier frequencies are configured in OverLaid subcell with the multiplexing mode of 1x3 being adopted, then the IUO cell is completely the same as the cell with the multiplexing mode of 1x3 adopted and the average frequency multiplexing ratio is the same as that of 1x3 multiplexing. Therefore, in this case, the IUO can effectively reduce the interference for the whole network and obtain the better network quality than 1x3 multiplexing without the decrease of network capacity.
The wider coverage can be realized through having the carrier in which BCCH is used large power amplifier. The power that provided by BCCH carrier is greater than other carriers, so the coverage distance of different carrier is different. While the cell coverage area depends on the carrier of smaller coverage, so the coverage area is greatly restricted. When the IUO technology is employed, the carrier with wide coverage can be used to serve as UnderLaid subcell to realize the far end coverage of site; while the carrier with small coverage can be used to serve as OverLaid subcell to increase the near end capacity of site. In this way, the cell coverage area can be increased.
Underlaid Overlaid
Figure 2-30 IUO coverage
Table 2-12 Coverage changes for typical sites after the employment of IUO cell Number of cell
carrier frequencies
Combining mode
Loss of low loss carrier
Loss of high loss carrier
Added coverage area after the employment of
IUO
3 CDU+CDU 1. 0dB 4. 5dB 27%
4,5 CDU+CDU+SCU 1. 0dB 8. 0dB 60%
4,5 CDU+CDU+CD
U 1. 0dB 4. 5dB 27%
5,6 CDU+CDU+SCU 4. 5dB 8. 0dB 27%
The division of OverLaid subcell and UnderLaid subcell is based on the MS downlink receiving level, downlink receiving quality and TA. The division of OverLaid subcell and UnderLaid subcell of common IUO is based on the "RX-LEV Thrsh." and "RX-LEV Hysteresis". The division of OverLaid subcell and UnderLaid subcell of enhanced IUO is based on the "U to O HO received level Thrsh." and "O to U HO received level Thrsh.". as shown in Figure 2-31.
Figure 2-31 Division of OverLaid subcell and UnderLaid subcell in a common IUO cell
Note:
The division foundation of OverLaid subcell and UnderLaid subcell is as follows:
OverLaid subcell:
Receiving Level>= RX_LEV Thrsh. + RX_LEV Hysteresis and
TA<TA Thrsh – TA Hysteresis and Receiving Quality < Receiving Quality Thrsh.
UnderLaid subsell:
Receiving Level < RX_LEV Thrsh. – RX_LEV Hysteresis or TA >=TA Thrsh + TA Hysteresis or Receiving Quality >= Receiving Quality Thrsh.
RX_LEV Thrsh., Receiving Quality Thrsh. and TA Thrsh. can be adjusted through data configuration. Therefore, under the precondition of without affecting the network performance indexes, the boarders of UnderLaid subcell and OverLaid subcell can be adjusted flexibly to let OverLaid subcell and UnderLaid subcell rationally share the traffic.
Receiving Quality Threshold U to O HO received level Thrsh.
O to U HO received level Thrsh.
Underlaid subcell
Overlaid subcell TA Threshold
TA Hysteresis
Figure 2-32 Division of OverLaid subcell and UnderLaid subcell in a enhanced IUO cell
Note:
The division foundation of OverLaid subcell and UnderLaid subcell is as follows:
OverLaid subcell:
Receiving Level>= U to O HO received level Thrsh. and
TA<TA Thrsh – TA Hysteresis and Receiving Quality < Receiving Quality Thrsh.
UnderLaid subsell:
Receiving Level < O to U HO received level Thrsh. or TA >=TA Thrsh + TA Hysteresis or Receiving Quality >= Receiving Quality Thrsh.
1) Channel assignment technology of IUO cell
This technology can adopt different assignment strategies in various channel assignment cases in fully consideration of features of IUO. The following are the main cases:
a) Immediate assignment
System assigns channel through access_delay in Channel Request message. System assigns the channel in overlaid subcell for the MS in the overlaid subcell; system assigns the channel in underlaid subcell for the MS in the underlaid subcell. System always selects the appropriate service layer for MS.
There is no reference receiving level, receiving quality and TA for immediate assignment. In order to guarantee the service quality, the SDCCH of UnderLaid subcell is assigned preferentially. Only when there is no signaling channel available in the UnderLaid subcell, will the signaling channel in the OverLaid subcell be assigned.
b) Assignment
The channel assignment strategy of IUO is used to assign channels. The OverLaid subcell channel will be assigned as far as possible when the subscriber is in the OverLaid subcell coverage. The UnderLaid subcell channel will be assigned when no OverLaid subcell channel is available. Similarly, the UnderLaid subcell channel will be assigned as far as possible when the subscriber is in the UnderLaid subcell coverage.
The OverLaid subcell channel will be assigned when no UnderLaid subcell channel is available. Select the suitable service layer to serve the subscriber.
c) Intra-BSC handover
Intra-BSC handover is applicable to the non-IUO handover and the handover from the OverLaid subcell directly to an adjacent cell. Use the IUO channel assignment strategy to assign channels and select the suitable service layer to serve the MS.
d) Inter-BSC handover
Being unable to get the receiving level, receiving quality and TA of adjacent cells, the system selects the preferential UnderLaid subcell, or preferential OverLaid subcell, or non-strategy mode through switch.
2) IUO cell handover technology
Huawei handover algorithm has the IUO handover judgement function to realize the IUO technology. When the MS crosses the boundary between OverLaid subcell and UnderLaid subcell, the IUO handover can be initiated to enable the MS to setup a call at a suitable service layer. If the object handover layer is congested, the handover will not be initiated. With the IUO cell handover technology, BSC can intelligently direct the traffic so as to utilize the frequency resource effectively.
III. Parameter
Parameters in [Handover/ Concentric Cell Handover Table]:
"Direction for IUO HO – UL to OL HO Allowed"
"Direction for IUO HO – OL to UL HO Allowed"
"Criterion for IUO HO – Rx_Lev for UO HO Allowed"
"Criterion for IUO HO – Rx_Qual for UO HO Allowed"
"Criterion for IUO HO – TA UO HO Allowed"
"UO signal intensity difference "
"RX_LEV Thrsh."
"RX_LEV Hysteresis"
"Receiving Quality Thrsh."
"TA Thrsh."
"TA Hysteresis"
"IUO HO Watch Time"
"IUO HO Valid Time"
"Assign optimum layer"
"Assign-optimum-level thrsh."
"Assign-Optimum-TA Thrsh"
"TA pref. Of Imme-Assign Allowed"
"Pref. subcell in HO of intra-BSC "
"Enhanced IUO allowed"
"O to U HO received level Thrsh."
"U to O HO received level Thrsh."
"U to O Traffic HO Allowed"
"Traffic Thrsh. of underlay"
"Underlay HO Step period"
"Underlay HO Step level"
"Penalty Time of U to O HO (S)"
Parameters in [Handover/Penalty Data Table]:
"Penalty time after IUO HO Fail."
Parameters in [Handover/Cell Description Data]:
"Cell Type"
Parameters in [Site/Carrier Configuration Table]:
2.2.5 "HW-IUO Property"Satellite Transfer
I. Technical description
Satellite communication is the development and the special form of microwave communication, the supplement and backup to conventional communication means.
Satellite communication features wide coverage, little effected by landform, fine mobility, and flexible link calling. Meanwhile, it has the problems such as delay, jitter, and bit error, which leads to the Abis interface of ordinary GSM equipment not supporting satellite transfer.
Huawei BSS adopts dedicated satellite transfer equipment to realize the satellite transfer of Abis interface according to the features of satellite transfer. The solution principle is described as follows:
1) LAPD protocol processing
During the LAPD protocol process, the timer duration is prolonged and the value of slide window is increased to resist delay.
2) TRAU frame algorithm
The adjustment algorithm of the TRAU frame is modified from fixed cycle adjustment to self-adaptive adjustment.
3) BTS clock work mode
The transmission between BSC and BTS can only occupy 19 time slots of DDN circuit (TS1~18, TS31) and the time slot 0 of DDN circuit is used for the synchronization of DDN instead of transmitting service. Therefore, BTS can only use the clock of DDN.
However, the accuracy of DDN clock is only 10E-7, which cannot satisfy the requirement of GSM protocol. BTS adopts internal clock, which accuracy meets the requirement of GSM protocol.
4) Voice quality
When the transmission bit error is less than 10E-6, the Voice quality is not affected.
Usually, the transmission bit error of satellite circuit is less than 10E-8.
As the link lease is very expensive and the quality is particularly sensitive to environments, the solution of Abis interface transmission by using satellite transfer should be positioned for the special areas where the ordinary transmission means is dissatisfactory and for the emergency communication. When the satellite transfer is used for networking, the star networking mode is usually adopted. The typical satellite transfer networking diagram is shown in Figure 2-33.
SDH/PDH /HDSL/Microware /E1
E1
E1
MSC Earth Station
BTS
BTS
BTS
BTS Satelite
Earth Receiving Station BSC
Earth Receiving Station
Figure 2-33 Typical satellite transfer networking diagram
Satellite communication is composed of satellite and ground station.
Generally, the satellite communication adopts synchronous satellite, i.e. the satellite
cycle is the same as that of the earth. The satellite consists of control system, communication system (antenna and trunk equipment), telemetry system, power supply system and temperature control system.
The ground station consists of antenna system, transmitter, receiver, channel terminal equipment (modem), communication control system and power supply system.
The ground station of ordinary satellite communication is a kind of large-sized international or European standard communication station. It has such features as high transmission rate, antenna of large caliber, and expensive cost of equipment. The subscriber data are connected to the ground station through the ground communication network to complete communication.
The subscribers in VSAT system form a dedicated network to communicate through satellite respectively. This mode is featured by its low cost of equipment, antenna of small caliber, and flexible application.
II. Parameter
1) “Transfer Mode ” in [Site\Site Description Table]
2) “Immediate Assignment opt ” in [Cell\Cell Call Control Table]
3) “MS MAX retrans ” in [Cell\System Information Table]
4) “Tx-integer ” in [Cell\System Information Table]
5) “CCCH_CONF ” in [Cell\System Information Table]