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Access Transmission Network Upgrade in a Nationwide Mobile Network Modernization Project for EDGE Deployment Attila Hilt, Péter Petrás, Dean Emsley, Grzegorz Rybarczyk
Abstract— In this paper details of a nationwide fixed access transmission network upgrade is presented with special focus on GSM network modernization for EDGE (Enhanced Data rates for GSM Evolution) deployment. Index Terms—mobile networks, fixed access transmission, GSM, EDGE deployment, MW links, modernization, upgrade
M
I. INTRODUCTION
OBILE telephony systems have been initially developed for circuit switched (CS) voice traffic. As early digital mobile systems were deployed for pure voice services they could not support actual user expectations in data services without modernization. Strong demand for new type of user services such as mobile internet access or mobile data down and upload resulted in continuous development of existing GSM networks. New services like mobile banking via WAP (Wireless Application Protocol), MMS (Mobile Multimedia Services), mobile internet, video streaming or mobile TV require more efficient networks providing higher and higher data rates. In recent years, continuous upgrade of mobile networks in terms of hardware (HW) and software (SW) of existing components as well as introduction of new network (NW) elements enable high data rates in actual GSM networks. First European GSM networks are typically older than a decade nowadays. Consequently the modernization and optimization of existing GSM networks give a continuous job for operators, equipment vendors and service providers. Several replacement projects were running in Europe where old equipment has been swapped out, changed or upgraded for latest hardware and software products enabling new services, more efficient network operation and maintenance resulting in significant cost savings. In the paper analysis of a nationwide GSM network modernization is given with special focus on the fixed access transmission (TRS) subsystem part.
Manuscript received February 29th, 2008. Attila Hilt and Péter Petrás are with Network Planning and Optimization, Nokia Siemens Networks Kft., H-1092 Budapest, Köztelek utca 6., Hungary (e-mail:
[email protected],
[email protected]). Dean Emsley is with Nokia Siemens Networks Austria, Vienna, (e-mail:
[email protected]). Grzegorz Rybarczyk is with Nokia Siemens Networks Poland, Warsaw, Poland (e-mail:
[email protected]).
II. MOBILE NETWORK EVOLUTION FOR DATA SERVICES The first technology supporting data calls in GSM was High Speed Circuit Switched Data (HSCSD). Next evolution step was General Packet Radio Service (GPRS), which employs packet-switching (PS) protocols in GSM networks. Supporting GPRS in GSM networks, SGSN (Serving GPRS Support Node) and GGSN (Gateway GSN) have to be installed as shown in Fig.1. Packet Switched core SGSN
GGSN
Gn BTS Gb
A
A-bis BSC BTS
MSC or MSS & MGW Circuit Switched core
Fig. 1. Architecture of the GSM network supporting PS data services
GGSN provides interworking functions with external PS networks. SGSN on the other hand, keeps track of individual mobile stations’ location and provides security and access control. The advantage of GPRS compared to HSCSD is in the efficient resource utilization. One GSM air-timeslot (TSL) can be shared between several GPRS users. High Speed Downlink/Uplink Packet Access
HSDPA
Universal Mobile Telecommunication Services Enhanced Data Rates for GSM Evolution General Packet Radio Service High Speed Circuit Switched Data Wireless Application Protocol Short Message Service
SMS 1997
WAP, HSCSD 1999 1998
~40 kbit/s
GPRS 2000
UMTS
2006 1.8 Mbit/s
EDGE
2003
2002
384 kbit/s
236.8 kbit/s (MCS.9)
48 kbit/s (CS.2)
GSM Evolution
Fig. 2. GSM / UMTS data staircase and available user throughputs
HSUPA 2007
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Fig.2 shows the evolution steps of mobile data services. EDGE became the next step after HSCSD and GPRS to provide data services with further increased user throughputs (TP) [1-6]. The Gaussian Minimum Shift Keying (GMSK) modulation method of GSM is replaced with eight-state Phase Shift Keying (8-PSK) in EDGE [5]. Due to three bits that are sent in one symbol, 8-PSK allows higher bit rate, as shown in Fig.3. 8 PSK
GMSK
(0,1)
(0,0,0)
(0,1,0) (0,1,1)
(0,0)
(1,1)
(0,0,1)
(1,1,1) (1,1,0)
(1,0,1) (1,0)
(1,0,0)
Fig. 3. Modulation schemes for GSM (GMSK) and EDGE (8-PSK)
The price paid for higher bit rates is the smaller coverage that affects the radio frequency (RF) network planning. EDGE and GSM use the same 200 kHz carrier spacing so they coexist within mobile networks. The main differences between EDGE and GPRS are summarized in Table I [1-5]. EDGE allows up to 59.2 kbit/s user throughput per air-TSL. Increased user mobile data rates require increased capacities in the fixed access TRS NW serving the base stations (BTS) [6-8].
TABLE II
TABLE I COMPARISON OF GPRS AND EGPRS THROUGPUTS Modulation
GMSK
8-PSK
unit
Number of bits
1
3
bit/symbol
Symbol rate
270.833
270.833
ksymbol/s
Air IF burst size
114
348
bit
Gross rate/air-TSL
22.8
69.6
kbit/s
User TP/air-TSL
14
59.2
kbit/s
236.8
kbit/s
Max. user TP/air-4TSL 56
arranged so that the standard GSM transceivers (TRXs) are connected to the BSC in the conventional way. Dedicated traffic channels (TCH) are allocated for standard CS services e.g. speech. Bits are reserved permanently for signalling (e.g. TRXSIG and BCFSIG). The dynamic A-bis transmission solution saves the A-bis TRS capacities as it allows A-bis dimensioning to be performed rather to the average instead of peak data rates. This also applies to the number of 2 Mbit/s interfaces needed in the BSCs, called ETs (exchange terminals) ports. Dynamic A-bis is implemented as a software feature [9, 10]. In the base stations EDGE capable TRXs are required, that support the 8-PSK modulation (Fig.3). For GSM/EDGE TRXs the BSC allocates the A-bis capacity for data calls from the EDGE Dynamic Abis Pool (EDAP) when needed i.e. when coding MCS-3 or higher is used. EDAP is an extra TSL territory in the A-bis that are shared by a number of EDGE TRXs. The size of EDAP territory is based on proper network dimensioning, and should reflect the users’ traffic on EDGE capable sites, e.g. 6 EDAP TSLs for dense urban sites and 4 EDAP TSLs for rural sites where less data calls are expected. Sometimes there is enough free TRS capacity available for EDAP allocation. In other cases the A-bis is already full-up and there is no available space at all. Table II shows an example where 2 sites are using the same 2 Mbit/s channel and each site has a 2+2+2 configuration. The sites are “groomed” as they share the same TRS resource of one single E1.
III. DYNAMIC A-BIS ALLOCATION CONCEPT As data rates in EDGE vary from 8.8 to 59.2 kbit/s over the air-TSL, traditional static A-bis allocation would not use the available TRS resources efficiently. Therefore dynamic Abis allocation concept was introduced. Dynamic A-bis allocation is a solution for higher data rates of EGPRS to ensure cost-efficient and flexible use of A-bis transmission capacities. Dynamic A-bis uses existing A-bis more efficiently by splitting the 2 Mbit/s frames (“E1s” or “PCMs”) into permanent timeslots for signalling and voice or data, and a dynamic pool only for data. The dynamic A-bis functionality allocates additional A-bis TSLs to air-TSLs only when needed instead of reserving fixed TRS capacity for the air-TSLs. The same pool can be shared by a number of transceivers. Using dynamic A-bis concept, a considerable saving in TRS network expansion is possible. The A-bis timeslot mapping is
TWO SITES OF 2+2+2 CONFIGURATION GROOMED INTO 1 E1 TS 1 2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 BTS1 : TRX SIG 1 26 BTS1 : TRX SIG 2 27 BTS1 : TRX SIG 3 28 BTS2 : TRX SIG 1 29 BTS2 : TRX SIG 2 30 BTS2 : TRX SIG 3 31 Pilot BTS1 Pilot BTS2
3
4 5 Link Management
6
7
8
MCB
LCB
BTS1 : TRX 1 Traffic Channel BTS1 : TRX 2 Traffic Channel BTS1 : TRX 3 Traffic Channel BTS1 : TRX 4 Traffic Channel BTS1 : TRX 5 Traffic Channel BTS1 : TRX 6 Traffic Channel BTS2 : TRX 1 Traffic Channel BTS2 : TRX 2 Traffic Channel BTS2 : TRX 3 Traffic Channel BTS2 : TRX 4 Traffic Channel BTS2 : TRX 5 Traffic Channel BTS2 : TRX 6 Traffic Channel BCF SIG 1
BCF SIG 2
BTS1 : TRX SIG 4 BTS1 : TRX SIG 5 BTS1 : TRX SIG 6 BTS2 : TRX SIG 4 BTS2 : TRX SIG 5 BTS2 : TRX SIG 6
TSL 0 is 64 kbit/s allocated for link management. Pilot bits in TSL31 are used if the TRS network is designed for loop-protecting the sites [8].
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As seen in Table II, there is no available space inside this E1 for EDAP at all, so only GPRS calls are supported. In this case the sites must be “ungroomed” before implementing EDGE. Ungrooming means that on the A-bis a new 2 Mbit/s path is required and each site will have its own separate E1. There will be then sufficient place for EDAP as well as for possible future TRX upgrades (e.g. from existing 2+2+2 site configuration to 3+3+3). The A-bis allocation for this ungrooming example is shown in Table III (a) and III (b). Pilot bits in TSL 31 are used when the TRS network is designed for loop-protecting the sites [8]. Clock bits (MCB, LCB) are reserved for clock distribution purposes that is required for synchronization. In Table II signalling (TRXSIG and BCFSIG) used 16 kbit/s. As indicated in Table III, TRX and BCF signalling speed was increased up to 32 kbit/s after ungrooming the sites. TABLE III (a) BTS1 OF TABLE II UNGROOMED INTO A SEPARATE E1 TS 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
1
2
3
4 5 Link Management
6
7
8
BTS1 : TRX 1 Traffic Channel BTS1 : TRX 2 Traffic Channel BTS1 : TRX 3 Traffic Channel BTS1 : TRX 4 Traffic Channel BTS1 : TRX 5 Traffic Channel BTS1 : TRX 6 Traffic Channel BTS1 : TRX 7 Traffic Channel BTS1 : TRX 8 Traffic Channel BTS1 : TRX 9 Traffic Channel
Pilot 1
BTS1 : TRX SIG 9 BTS1 : TRX SIG 7 BTS1 : TRX SIG 5 BTS1 : TRX SIG 3 BTS1 : TRX SIG 1 MCB
TABLE III (b) BTS2 OF TABLE II UNGROOMED INTO A SEPARATE E1 TS 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
1
2
3
4 5 Link Management
6
7
8
BTS2 : TRX 1 Traffic Channel BTS2 : TRX 2 Traffic Channel BTS2 : TRX 3 Traffic Channel BTS2 : TRX 4 Traffic Channel BTS2 : TRX 5 Traffic Channel BTS2 : TRX 6 Traffic Channel BTS2 : TRX 7 Traffic Channel BTS2 : TRX 8 Traffic Channel BTS2 : TRX 9 Traffic Channel
Dynamic Abis Pool
BTS2 : TRX SIG 8 BTS2 : TRX SIG 6 BTS2 : TRX SIG 4 BTS2 : TRX SIG 2 BCF SIG 2 Pilot 1
BTS2 : TRX SIG 9 BTS2 : TRX SIG 7 BTS2 : TRX SIG 5 BTS2 : TRX SIG 3 BTS2 : TRX SIG 1 MCB
LCB
As a result of ungrooming there is now space for future TRX upgrades in BTS2 too. Similarly to BTS1 an EDAP of 6 A-bis TSL is allocated. Actual site configuration remained also 2+2+2 (6 TRXs) but there is a possibility to upgrade BTS2 to a site configuration of 3+3+3.
Dynamic Abis Pool
BTS1 : TRX SIG 8 BTS1 : TRX SIG 6 BTS1 : TRX SIG 4 BTS1 : TRX SIG 2 BCF SIG 1
answer : What transport sections must be upgraded (SDH, PDH, Leased Lines (LL), microwave (MW) links) and how. Can capacity upgrade be performed by simple SW activation on the existing network elements? Is HW extension achievable if simple SW activation is not possible (e.g. by adding more transmission cards) or is equipment swap required?
LCB
As a result of ungrooming there is now sufficient space for future TRX upgrades in BTS1 (TSL13-TSL18). Actual site configuration remained 2+2+2 (6 TRXs) but there is a possibility to upgrade the site to 3+3+3. An EDAP of 6 A-bis TSL is allocated that can be later expanded in TSL 25 if data traffic increase requires so.
In the presented example a new 2 Mbit/s channel was required in the fixed access TRS NW in order to activate EDGE on two base stations. During a mobile network modernization project it is a crucial dimensioning question to find out how many such or similar transmission capacity upgrades are required for EDGE deployment. When capacity upgrades are required detailed planning should provide the
After the implementation of EDGE it is the task of radio and transmission optimization engineers to monitor continuously and investigate Key Performance Indicators (KPIs) that are based on BSC counters. KPI and counter analysis as well as drive tests may show congestions or unexpectedly slow data speeds (discarded frames or retransmissions etc.) at different points of the network. KPI monitoring may lead to further increase (or decrease) of EDAP size after careful investigation of the specific problem. IV. REQUIRED TRANSMISSION NETWORK UPGRADES FOR EDGE DEPLOYMENT The main task of the fixed access network is to provide the A-bis interface connecting sites to BSCs (Fig.1). A typical GSM/UMTS access network is composed of PDH and SDH sections. The physical media are microwave radio links, optical fibers (either SDH sections or “dark fibers” that are part of the operator’s own network or provided as leased lines)
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and copper cables (typical for LL). Before the activation of EDGE service the proper transmission capacity must be ensured when old base stations (or not EDGE capable BTS transceivers) are replaced by new EDGE capable ones. The entire BSC-BTS transmission chain (or loop) must be checked and different type of access TRS upgrades may be required. For the better visibility of necessary TRS NW modifications in a nationwide project, it is useful to classify the different types of possible upgrades. Table IV gives an overview of potential TRS upgrades with their short explanation. The order of the listed TRS problems reflects their complexity. TABLE IV DIFFERENT TYPES OF TRANSMISSION NETWORK UPGRADES D1 :
“Easy swap” site. Existing transmission capacity is sufficient to activate EDGE after the site is upgraded or swapped. No additional 2Mbit/s (E1) required.
D2 :
Existing physical transmission capacity is sufficient, but new 2 Mbit/s path must be “patched”. Patching means either remote electrical cross-connections or local physical cabling on sites. The entire new A-bis 2 Mbit/s path must be established and checked between BSC ET port and BTS before EDGE activation. Good example of D2 is the “ungrooming”, where two (or more) sites are sharing the same E1 where there is no sufficient A-bis TSL available for EDAP but there is free capacity available as an other E1. Please see the example of Table II and Table III.
D3 :
The A-bis path contains SDH section, where additional 2 Mbit/s must be allocated for the BTS. SDH provisioning may require either simple activation of existing physical interfaces or upgrade e.g. insertion of new interface card(s) into existing SDH transmission network element(s). Typical example is the re-commissioning or upgrade of Add Drop Multiplexer (ADM).
D4 :
Microwave link(s) must be swapped or capacity upgraded. Capacity increase on existing MW link(s) or swap of old MW links requires interference calculation and frequency licensing procedure with the local Communication Authority.
D5 :
Leased line capacity upgrade is required.
D6 :
BSC problem: no more free ET card/port is available in the actual BSC or PCU full-up. Sometimes BSC is frozen due to other reasons e.g. BSC rehoming activities or software upgrade for latest BSC SW release.
D7 :
Core network upgrade is required (e.g. SGSN or Gb interface, connectivity or capacity upgrade).
A very important conclusion is that one site may have several transmission problems, like “D2D4D6”. In general, the number of sites are not equal to the number of TRS problems. On the other hand, the successful elimination of a transmission problem can solve the TRS problem of several other sites. E.g. when a site requires MW link upgrade (D4) and the MW link capacity is increased e.g. from 8x2 to 16x2 Mbit/s the remaining free capacity of the upgraded MW link can carry EGPRS (or UMTS) traffic of several other sites too.
V. NETWORK EXAMPLE FOR EDGE DEPLOYMENT A. Statistics of Transmission Network Modifications for Site Swaps and EDGE Activations A Swiss operator improved its mobile network performance by replacing old base stations to new EDGE capable ones in order to provide high speed data services. The EDGE upgrade project was divided into two phases. Phase 1 covered the capital and main cities by EDGE upgrade of 800 sites. Phase 2 covered the rest of the country by EDGE upgrade of 1202 sites. During the project altogether 2002 BTS were swapped or upgraded and EDGE activated. More than 20 BSCs were replaced or capacity extended. All BSCs were upgraded for latest SW version [9, 10] and one SGSN was extended too. Fig.4 shows the sites divided into two types: dots are sites upgraded to EDGE without encountering any TRS difficulty (D1). Squares show sites where improvement of existing TRS network was necessary before EDGE launch (D2…D7 sites).
Fig. 4. Sites swapped and upgraded for EDGE
Table V and Fig.5 summarize the statistics and regional distribution of different TRS problems experienced in the project. More than 13% of the sites initiated additional capacity allocations over the SDH backbone and nearly 11% of the sites required upgrade or swap of the existing MW links. TABLE V STATISTICS OF DIFFERENT TRANSMISSION NETWORK UPGRADES EXPERIENCED IN THE SWISS EDGE DEPLOYMENT PROJECT TRS problems
East
West
Total
D1
972
514
1486
74.2 %
D2
228
199
427
21.3 %
D3
137
130
267
13.3 %
D4
103
116
219
10.9 %
D5
31
17
48
2.4 %
D6
53
17
70
3.5 %
Number of problems 1524
993
2517
% of sites
125.7%
Table VI shows the different combination of TRS problems encountered during the EDGE deployment. As seen in Table
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VI, 74.2% of the sites were ready for EDGE upgrade and activation without any TRS problems (D1 sites). Roughly 26% of the sites had one or more TRS problems. The total number of solved TRS problems exceeded 1000. 500 East 400
West Total
300 200 100
Site Swaps and EDGE Activations The roll-out has been finished in a very short timeframe of one and a half year. Fig.6 shows the number of sites swapped and EDGE activated per week. There were three different kind of EDGE activations possible on a site. The easiest is the SW activation. In this case the BTS operated already with EDGE capable TRXs but EGPRS was disabled. There EDGE was turned on by local site configuration or via OSS remotely. In several cases the BTS cabinet itself supported EDGE capable TRXs but new EDGE TRXs had to be inserted (TRX extension or TRX swap). In the most difficult case the BTS cabinet was old and was not able to support EDGE. In this case the entire BTS was swapped out and replaced with a new BTS cabinet equipped immediately with EDGE TRXs. 80
0 D2
D3
D4
D5
D6
Fig. 5. Distribution of different TRS network upgrades in the regions
60
Table VI shows that only 8.2% of the sites had one single TRS problem (D2 or D4). Remarkable, that the majority of the TRS difficulty sites had combined TRS problems e.g. simultaneous need for patching, LL upgrade and BSC extension (D2D5D6) or patching combined with MW and SDH upgrades (D2D3D4). It is also important to mention that a lot of MW link upgrades (D4) and cross-connections could be done without physical site visits and cabling (D2). State-of-the-art MW radios provide remote management possibility and remote electrical cross-connection feature [11, 12]. In all other cases (D3, D5, D6) patching and cabling work (D2) was all the time necessary on the sites.
50
TABLE VI DIFFERENT TYPES OF THE TRANSMISSION PROBLEM SITES EXPERIENCED IN THE SWISS EDGE DEPLOYMENT PROJECT TRS problem sites
East
West
Total
%
D2
38
43
81
4.0 %
D2D3
57
53
110
5.5 %
D2D3D4
36
61
97
4.8 %
D2D3D4D6
6
1
7
0.3 %
D2D3D5
17
5
22
1.1 %
D2D3D6
21
9
30
1.5 %
D2D4
14
12
26
1.3 %
D2D4D6
6
1
7
0.3 %
D2D5
13
12
25
1.2 %
D2D5D6
1
0
1
0.0 %
D2D6
19
7
26
1.3 %
D4
41
43
84
4.2 %
TRS problem sites
269
247
516
25.8 %
D1 “easy swap” sites 972
514
1486
74.2 %
Total
761
2002
100%
1241
Number of sites swapped and EDGE activated per week
70
40 30 20 10 0 Week
5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 5/ 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 1 2 3
4 5 6
7 8
9
6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 6/ 1
1 1 1
1 1
1 1 1
1 2
2 2
2
2 2
0
1 2 3
4 5
6 7 8
9 0
1 2
3
4 5
2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
Fig. 6. Number of sites swapped and EDGE activated per week in the project
B.
Microwave Link Capacity Upgrades and Link Swaps Density of microwave links increased rapidly in the last decade mainly due to the quick expansion of mobile networks [8, 13-17]. Hundreds of 2G/3G base stations are connected to BSCs/RNCs over MW radio links thanks to the advantage of rapid implementation and relatively moderate monthly fees (e.g. compared to optical fiber implementation or monthly LL costs). Digital microwave radio (DMR) technology developed simultaneously with the strongly increasing demand.
Fig. 7. Swapped or capacity upgraded microwave links
State-of-the-art DMRs offer numerous advantages compared to older DMR versions. Possibility of remote
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control (e.g. setting the capacity, output power or transmit frequency, remote electrical cross-connection of transmitted digital signals, etc. [11-14]), error correction techniques, automatic transmit power control (ATPC), built-in bit-error (BER) testing make the network more reliable, flexible and cost effective as well as operation and maintenance easier. Nearly 500 microwave radio links have been replaced or capacity upgraded during the modernization project (Fig.7 and Fig.8). Several old DynaHopper radios were replaced by new FlexiHopper Plus or MetroHopper radios [11, 12]. Significant OPEX savings were realized with simultaneous capacity increase in the overall TRS network. The main task of the modernization project was to provide the extra TRS capacity required for EDGE deployment. Naturally, the remaining free capacities helped the operator in UMTS and HSDPA deployment. In practice most of the 2G and 3G sites are colocated so usually the same TRS NW is shared. During the design of the MW link swaps and upgrades, the latest regulations of the local Communication Authority were kept. 500 PLANNED MW LINKS
400
FREQUENCY APPROVED LINKS IMPLEMENTED MW LINKS LINKS TO BE BUILT / SWAPPED
300
200
100
0 1. 29. 27. 24. 22. 19. 16. 16. Sep. Sep. Oct. Nov. Dec. Jan. Feb. Mar. 2005 2006
13. 11. 8. 6. Apr. May. Jun. Jul. 2006
3. 31. 28. 26. 23. Aug. Aug. Sep. Oct. Nov. 2006 2006
Fig. 8. Number of microwave links planned, frequency licensed and implemented in the network
C.
Microwave Access Network Optimization Mature mobile operators heavily utilize the available access transmission network capacities [8, 13-17]. Any new capacity demand may unavoidably lead to optimization. Modernization projects inherently offer the possibility of optimizing dense MW access networks. There are some basic rules listed in Table VII that must be followed in order to achieve high spectral efficiency and better frequency re-use in MW radio access networks. Even though these rules are well-known they cannot be always followed, as real-life networks develop “evolutionary”. Mobile networks undergo continuous deployment and changes. New and newer sites are coming up and sometimes old sites are demolished. To provide the connection of the new sites new links must be added to the already existing dense MW network. Each new link requires interference calculation [15, 18-20] and the proper frequency is selected if possible. However, at a certain point of network complexity the developed network show interference when
new links are added and we cannot enter any new link without modifying some of the already existing links [13-17]. TABLE VII BASIC RULES FOR DENSE MW ACCESS NW DESIGN Rule Always select the proper frequency band. Long links should 1: use lower frequency bands e.g. 7, 8, 13, 15 or 18 GHz. Short links should use as high frequencies as possible : 23, 26, 32, 38 or 58 GHz (Fig.9) [11-14, 21-31]. In most of the EU countries there are local regulations forcing all the network operators for very efficient band selection [32, 33]. In Hungary, for example in the 23 GHz band the max. EIRP (Equivalent Isotropically Radiated Power) is EIRP=50 dBW only if D≥7 km. However, if D
