Abstract: This paper first introduces the CDMA network reference model. Then it introduces the planning method of switching network, including switching network organization, signaling network organization, signaling mode, numbering scheme and synchronization requirements. Finally, the planning method of wireless network is introduced, including frequency configuration and network planning steps.

1 overview

At present, the digital cellular system based on CDMA (code division multiple access) technology has made remarkable achievements in the world (especially in the United States, Hong Kong and South Korea) after more than two years of commercialization with its advantages of large capacity, good sound quality and great upgrade potential. In China, the former Ministry of Posts and Telecommunications and the Communications Department of the General Staff Department decided to jointly develop 800MHz CDMA digital cellular mobile communication at 1995, which is called China Telecom Great Wall Network. Since 1996, pilot networks have been built in Beijing, Shanghai, Guangzhou and Xi 'an. At present, these four experimental networks have been opened and roaming tests have been completed. The experimental network in Beijing has begun to be free of access fees. China Unicom Co., Ltd. has also started to build trial networks in Guangzhou, Tianjin and Shanghai from 1996, and it is expected to start networking testing soon. Both China Telecom and China Unicom have issued relevant technical systems and specifications. It is believed that CDMA, as a PLMN standard, will rise in the field of mobile communication in China in the near future.

2 network reference model

The CDMA network reference model defines the functional entities and interfaces in the network, which is similar to the GSM network.

MSC mobile switching center HLR home location register

VLR visits location register AC authentication center

MC SMS center SME SMS entity

Public switched telephone network mobile station

EIR equipment identification and registration base station system

IWF interconnection function of OMC operation and maintenance center

3 switching network planning

3. 1 switching network organization

The CDMA network adopts a three-tier structure, specifically: setting up a first-tier mobile service tandem center in regional centers (such as Beijing, Shanghai, Guangzhou, Shenyang, Wuhan, etc.). ) and connected into a mesh; Establish secondary mobile service tandem centers in provincial capitals or big cities and connect them with corresponding primary tandem centers; One or more mobile end offices MSC are set in the mobile service local network, and one MSC can also cover multiple mobile service local networks according to the traffic volume. In principle, the local network of mobile service is divided into 2-digit and 3-digit areas in the long-distance number of fixed telephone network.

3.2 Signaling network organization

At present, the signaling network of China Telecom and China Unicom's mobile communication network is specially set up, because it is necessary to transmit not only the t up message of telephone users, but also the MAP message of mobile applications.

The signaling network of CDMA network corresponds to its switching network structure, and it is also divided into three levels: high-level signaling transfer point HSTP, low-level signaling transfer point LSTP and signaling point SP.

HSTP is responsible for transmitting signaling services within this area and between this area and other large areas. HSTP can play the role of LSTP. LSTP is responsible for transferring the signaling service in this service area to its superior HSTP. SP is the source and destination of signaling messages.

The signaling transfer point STP can be an independent device or combined with the mobile tandem center.

China No.7 signaling is adopted between network nodes in the signaling network.

3.3 signal mode

Technical Specification for Air Interface of 800MHz CDMA Digital Cellular Mobile Communication Network stipulates the wireless signaling flow of Um interface (also known as air interface). Both China Telecom and China Unicom have issued this specification. This specification is based on TIA/EIA/IS-95A- mobile station-base station compatibility standard for broadband dual-mode spread spectrum cellular system.

The signaling flow of interface A is specified in Technical Specification for Interface Signaling between Mobile Service Switching Center and Base Station Subsystem of 800MHz CDMA Digital Cellular Mobile Communication Network. Both China Telecom and China Unicom have issued this specification. The signaling specification of interface A issued by China Unicom is basically compatible with the signaling specification of EIA/TIA/IS-634 and is a subset of it.

The signaling flow of interfaces B, C, D, E, N and P is specified in the mobile application technical specification of 800MHz CDMA digital cellular mobile communication network. Both China Telecom and China Unicom have issued this specification. This specification is based on TIA/EIA/IS-4 1C- Interoperability Standard for Cellular Wireless Communication Systems. The map published by China Unicom is a subset of IS-41C. The first stage uses 5 1 in IS-4 1C and1in operation, which is mainly used for authentication, handover, registration, routing request and short message transmission.

The technical specification of the interface between 800MHz CDMA digital cellular mobile communication network and PSTN network stipulates the signaling flow of Ai interface. Both China Telecom and China Unicom have issued this specification. This signaling process is also called MTUP. The MTUP issued by China Unicom is a subset of the signaling procedures stipulated in Technical Specification for Signaling Mode No.7 of China Domestic Telephone Network, that is, MTUP does not use NNC, SSB, ANU, CHG, FOT and RAN messages; In addition, only four messages were received but not sent: the follow-up address message SAM, SAO with the follow-up address message signal, the calling subscriber hang-up signal CCL and the subscriber local busy signal SLB.

3.4 numbering plan

(1) mobile phone number DN

When dialing the called number for a mobile user, the calling user needs to dial this number. DN consists of country code, mobile access code, HLR identification code and mobile subscriber number *** 12 digits. The country code of China is 86, which can be omitted when dialing in China. The mobile access code adopts the network number scheme, Great Wall Network 133 and Unicom 132. The difference between CDMA network and GSM network DN lies in the difference of mobile access code.

(2) international mobile subscriber identity IMSI and mobile station identity MIN

IMSI is the only number to identify mobile users in CDMA network, which consists of three parts: mobile country code, mobile network code and mobile user identification code *** 15 digits. The mobile country code of China is 460, and the mobile network codes of Great Wall Network and China Unicom are 03.

The minimum code is defined by AMPS standard to ensure CDMA/AMPS dual-mode operation. Great Wall Network and Unicom have different definitions of MIN. The great wall network is defined as 3h1h2h3×××××× year×× month×× day× month× day× month× day× month× day× month× day× month× month× day× month× day× month× day× month× month× day× month× month× day × month× month× month× day × month× month× day × month× month × day × month× month × day × month× month × month × day × month × month × day × month

(3) Electronic serial number ESN

ESN is a 32-bit number that uniquely identifies the mobile station equipment, and each dual-mode mobile station is assigned a unique electronic serial number, which consists of the manufacturer number and the equipment serial number. The signaling messages of air interface, A interface and MAP all use ESN.

(4) System identification code SID and network identification code NID

SID is a unique number that identifies the home network of mobile service in CDMA network. SID is allocated by province. NID is a unique number to identify the network in the mobile service local network, which can be used to distinguish different MSCs. The mobile station can judge its roaming status according to the SID and NID.

3.5 Synchronization requirements

(1) wireless synchronization requirements

CDMA system has strict requirements for wireless timing. IS-95 stipulates that the time error between pilot PN sequence and all Walsh sequences of the same forward CDMA channel should be less than 50ns；; The transmission time of different CDMA channels in the same base station must be within 1 μ s; The transmission time of the pilot PN sequence of all base stations must be within 10μ s, so every base station needs to use GPS as the time reference source.

(2) Network synchronization requirements

The purpose of network synchronization is to synchronize the frames of digital information flow between network nodes and ensure the normal transmission of voice, signaling and network management data.

The technical systems of Great Wall Network and Unicom CDMA network both stipulate that the GPS system is used as the clock reference in CDMA network, and the synchronization reference of public digital synchronization network is used as the backup clock reference.

The synchronization reference of the first-level mobile service tandem center and the second-level mobile service tandem center comes from the second-level class A bits. The synchronization standards of MSC, VLR, HLR and AC come from Class B bits. The BSC extracts the clock from the data stream from the MSC. BTS extracts the clock from the data stream from BSC.

4 wireless network planning

4. 1 frequency configuration

The working frequency bands of China Unicom CDMA network are 835 MHz ~ 839 MHz (received by base station) and 880 MHz ~ 884MHz (transmitted by base station), that is, 4MHz usable frequency, and the frequency interval between uplink and downlink is 45MHz. The basic CDMA channel is AMPS channel 384 (836.52MHz), and the second CDMA channel is 425 (837.75MHz).

The working frequency bands of Great Wall Network are 825MHz~835MHz (received by base station) and 870MHz~880MHz (transmitted by base station), that is, 10MHz available frequency, and the frequency interval between uplink and downlink is 45MHz. The basic CDMA channel is AMPS channel 283 (833.49MHz), and the second CDMA channel is channel 242 (832.26MHz). The extended CDMA channels are 20 1 (83 1.03MHz), 160 (829.80MHz),1/9 (828.57mhz) and 78 (827.34MHz).

4.2 wireless network planning steps

The goal of wireless network planning is to design the network economically on the premise of meeting the requirements of coverage, capacity and quality of service. In fact, it is planning a complicated process. The following is a simplified planning process.

(1) Define coverage requirements, capacity requirements and quality of service requirements.

Coverage requirements include the area to be covered. According to the terrain, the coverage area can be divided into high-density urban areas, general urban areas, suburbs, villages and expressways. At the same time, it is necessary to put forward the tourist attractions, airports and bustling commercial areas that need to be covered.

Quality of service requirements include frame error rate FER, radio channel call loss, handover rate, cell edge reliability, cell area reliability and so on. Capacity requirements can be put forward according to existing traffic distribution data (such as GSM) and growth forecast data.

(2) Estimate the number of base stations meeting the capacity requirements.

The limit capacity of a sector can be calculated by the following simplified formula (1).

Where: NMAX is the ultimate capacity; W/r is the processing gain; Eb/io is the ratio of bit energy to interference power density; VAF is a sound activation factor; F is the interference factor of other sectors to the current sector.

Generally, when VAF is 0.4, EB/IO is 7dB (corresponding to 1% FER), F is 0.85 (for three sectors), and NMAX is about 36.

The limit capacity in the formula (1) is the capacity when the distance between the mobile station and the base station tower is 0. The actual capacity should consider the sector load. The typical value of sector load is 40% ~ 75%.

According to the limit capacity and sector load, the maximum number of traffic channels can be calculated when the three-sector or omni-directional base station is configured at full capacity. Then, according to the call loss of wireless channel and the busy traffic of each user, the number of base stations needed to meet the given capacity can be estimated.

(3) Estimate the number of base stations meeting the coverage requirements.

Using link budget and appropriate propagation model to estimate the coverage radius of base stations, the number of base stations required for a given coverage area can be estimated. Table 1 shows the typical link budget.

Table 1 Contact Budget Table Project Unit Suburb Village in High-density Urban Area and General Urban Area

(a) the maximum transmission power of the mobile station

(b) mobile station antenna gain

(c) loss of personnel

Effective radiated power EIRP of mobile station.

(e) the base station receiving antenna gain

(f) the base station receives the feeder loss

(g) Noise figure of the base station receiver

(h) Noise density of the base station receiver

(1) Information rate (10log9.6k)

(j)Eb/Io

(k) Receiving sensitivity of the base station

(l) Interference tolerance (corresponding to 60% cell load)

(m) soft switching gain

(n) base station diversity gain

Fading margin

(p) building seepage loss

Maximum path loss (d-k+e-f-l+m+n-o-p)

dBm

decibel

decibel

dBm

dBi

decibel

decibel

dBm/Hz

dBHz

decibel

dBm

decibel

decibel

decibel

decibel

decibel

decibel

23

three

20

15.5

three

five

- 174

39.82

seven

- 122.2

3.98

3.5

5.5

28

120.7

23

three

20

15.5

three

five

- 174

39.82

seven

- 122.2

3.98

3.5

5.5

20

128.7

23

three

20

15.5

three

five

- 174

39.82

seven

- 122.2

3.98

3.5

5.5

15

133.7

23

three

20

15.5

three

five

- 174

39.82

seven

- 122.2

3.98

3.5

5.5

10

138.7

When HATA model is selected as the propagation model, the urban propagation loss is shown in Formula (2).

PL urban area = 69.55+26.16× log (f)-13.82× log (HB)-a (hm)+(44.9-6.55× log (HB) )× logr (2).

Where PL is the path loss (dB)

F is the frequency (MHz)

Hb is the antenna height of the base station (m)

Hm is the antenna height of the mobile station (m)

R is the distance (km) from base station to mobile station.

A(hm) is the antenna height correction factor of the mobile station.

For small and medium-sized cities, a (hm) = (1.1× log (f)-0.7) × hm-(1.56× log (f)-0.8).

For big cities, a (hm) = 3.2× (log (11.775× hm)) 2-4.97.

For suburbs, the modified formula of propagation loss is PL suburb =PL urban area -2× (log (f/28)) 2-5.4.

For rural areas, the revised formula of propagation loss is PL rural area =PL urban area-4.78× (logf) 2-18.33× logf-40.94.

(4) Steps (2) and (3) can quickly estimate the number of base stations at the initial stage of design. Select the maximum of the two, and initially determine the location of the base station.

(5) Using simulation tools to simulate and design each base station.

After the site selection is confirmed, simulation tools (such as Motorola's NetPlan, Lucent's CE4 and Nortel's PlaNet) are used to start the simulation.

The input of the simulation tool is:

. System parameters. Such as chip rate, paging rate, etc. ;

. Mobile station parameters. Such as noise figure, required EB/IO, etc.

. Cell/sector parameters. Such as pilot power, synchronization and paging channels, pilot PN offset index, pilot detection threshold T-add/T-drop, pilot search window, etc.

The simulation tool uses digital maps, and the common outputs after simulation are:

Pilot signal strength diagram. This diagram is a pilot signal strength analysis diagram of propagation loss;

EC/IO diagram of the strongest pilot. This diagram can analyze the coverage effect of the forward link;

Mobile station transmit power diagram. The mobile station can analyze the reverse link coverage effect in order to meet the minimum transmission power diagram required by the target EB/IO.

. Soft handover area map. The mobile station can perform soft handover area mapping and analyze the degree of pilot pollution at the same time.

According to the output results, it can be judged whether the design meets the requirements of coverage, capacity and performance, so that it can be adjusted from the following aspects:

Increase or decrease base stations;

Change the address of the base station;

Adjust the azimuth and inclination of the base station antenna;

Adjusting the transmitting power of the base station;

Adjust cell/sector parameters.

5 concluding remarks

The network planning of digital cellular mobile communication network involves wireless communication, switching, signaling, synchronization, billing, network management and other communication technologies, which is a systematic project. Scientific network planning will lay a solid foundation for subsequent operation, maintenance and management.

This paper briefly introduces several important aspects of CDMA network engineering design, and accumulates technology for future engineering design.