Yu.M. Tulyakov, D.Ye. Shakarov, A.A. Kalashnikov. Keywords: Data broadcasting, cellular mobile systems, WCDMA, GSM.

Transcription

1 Аnalysis of data broadcasting in modern cellular mobile systems of ground radio communications Yu.M. Tulyakov, D.Ye. Shakarov, A.A. Kalashnikov At the analysis of channel formation in WCDMA networks the special attention is turned to broadband messages transmission. Data transmission rates are denoted and main WCDMA and GSM networks characteristics are compared, enabling more precise organization of broadcast data transmission and limiting possibilities of this transmission that is important at the organization of services of the mass notification of the population. Keywords: Data broadcasting, cellular mobile systems, WCDMA, GSM. Modern cellular systems can deliver messages to all subscribers who are in the system coverage area. This zone (the area) may be limited to one base station sector, it can include multiple sectors or cover the entire territory. CellBroadcast (broadcast messages) is focused on multicast messaging in a fixed geographical area. Parameters of the broadcast messages are the same for GSM network (GlobalSystem for Mobile Communications), and for the UMTS network (Universal Mobile Telecommunications System). Number of CellBroadcast channels is determined by three-digit numeric identifier. Each channel can consist of 15 pages, each page consists of 82 characters in Roman letters or 41 characters in the Cyrillic alphabet. Total length of one message is 1230 characters in Latin or 615 characters in the Cyrillic alphabet. Each message has an ID that is listed on all pages of one message. Using this information, MS / UE (Mobile Station / User Equipment) is able to identify and ignore already received messages [1]. GSM Radio standard is described in many publications (eg [5,6,7]). This article focuses on the radio interface of third generation WCDMA (Wideband Code Division MultipleAccess) of the UMC network. In WCDMA bits of information are converted to a sequence of bits (pulses), which is called a chip. This sequence is an extension code. As a result, the broadband signal is generated. Transmission rate is 3.84 Mchips/s, it takes a band of approximately 5 MHz. WCDMA supports different data transfer rates. Data is transmitted in frames, transmission duration is 10 ms, for each frame data rate remains the same. However, transmission capacity for the user can change from frame to frame. WCDMA supports two basic modes: FDD - Frequency Division Duplex TDD - Time Division Duplex. FDD mode uses separate carriers with a bandwidth of 5 MHz, whereas in the TDD mode, only one carrier with a bandwidth of 5 MHz is used with the time division of receiving and transmission [2]. WCDMA uses three types of channels - logical, transport and physical. Logical channels transmit data at the MAC (Media Access Control) level. Logical channels exist for different types of data transfer offered by MAC level. Each type of logical channel is determined by the type of information transmitted. Logical channels are divided into two groups: control channels and transmission channels (Fig. 1). Control channels are divided into: BCCH - Broadcast Control Channel PCCH - Paging Control Channel

2 DCCH - Dedicated Control Channel CCCH - Common Control Channel. This logical channel is always converted to transport channels RACH (Random Access Channel / FACH (Forward Access Channel). Traffic channels are divided into: DTCH - Dedicated Traffic Channel. It is a channel between the base station and the UE for a subscriber to transmit or receive information. CTCH - Common Traffic Channel. Channel from one point to many points to pass information to all or certain groups of subscriber units UEs [3]. CTCH channels are necessary for broadcasting. Figure 1. The structure of the WCDMA logical channel Logical channels overlap on the physical channels through the transport channels. Options for applying logical channels transport are shown in (Fig. 2). Transport channels are divided into: single channels and common channels. Common channels provide their resources to all users or groups of the cell. Dedicated channels are only available to one user. Main transport links are considered: BCH - Broadcast Channel is the transport channel that carries a special information for the entire network or only for this cell (cell). Data is transmitted with high power and low fixed speed, and all users of the cell can receive the data FACH - Forward Access Channel is a transport channel, which operates terminals in the cell. This channel can transmit user data. There maby be a few FACH channels in the cell. If more than one FACH channels is in use, one of direct access channels should have a little speed, so all terminals in this cell could take it. Additional channels may have higher transmission rates than FACH. FACH channel is multiplexed with the PCH - Paging Channel in the same physical channel, but may be separate. PCH is a transport channel that carries the search message when the network needs to communicate with the subscriber unit. RACH transmits information from the terminal of the base station. The main task of this channel is the transmission of connection requests. However, this channel can be used for transferring small amounts of data from the terminal to the network. CPCH - Common Packet Channel is a channel for transmitting data from the user.

3 DSCH - Downlink Shared Channel is the transport channel for transmitting the selected data to the user and control information. This channel can be used by multiple users. DCH (Dedicated Channel is the transport channel, it works in both directions (uplink and downlink). Control information for the higher levels, and user information is transmitted through this channel Fig. 2 shows the channels involved in the broadcasting. Figure. 2. Interaction (overlap) of logical channels and transport channels Transport channels at the lowest level overlap on the physical channels (see Fig. 3). Physical channels support the work of transport channels with variable speed. Physical control channel transmits information about the active transport channels. Physical channels are divided into dedicated and common: DPDCH Dedicated Physical Data Channel; DPCCH Dedicated Physical Control Channel. Dedicated transport DCH is superimposed on the DPDCH and DPCCH. DPCCH carries control information: power control, feedback command, the transport format indicator. Speed and power transmission of this channel is constant. DPDCH carries user information, it can have a variable speed. Multiple channels DPDCH can have one DPCCH. PCCPCH Primary Common Control Physical Channel is used for the organization of BCH. PCCPCH alternates c SCH (Synchronization Channel) SCCPCH Secondary Common Control Physical Channel, FACH carries and the drive information Physical Random Access Channel (PRACH) is used when the terminal wants to request network resources to transmit any information. Physical Downlink Shared Channel (PDSCH) Physical Common Packet Channel (PCPCH) Synchronization Channel (SCH) consists of two sub-channels: primary and secondary SCH. Used to search only the cells. Common pilot channel (CPICH) Acquisition Indicator Channel (AICH). Powered by downlink with the PRACH. Page Indicator Channel (PICH) CPCH Status Indicator Channel (CSICH)

4 Collision Detection / Channel Acquisition (CD / CA - ICH). Figure. 3. Imposition transport channels to physical channels Figure 3 shows the channels involved in the broadcast. Broadcast messages are transmitted through the logical CTCH. At the RNC (Radio Network Controller) module BMC (Broadcast / Multicast Control) is responsible for processing, scheduling and transmission of broadcast messages. FACH does not transmit information at high rates, therefore, FACH has a constant expansion factor. RNC controls the transmission of data on FACH. FACH data is transmitted by an additional common control channel at the physical level (SCCPCH). At SCCPCH two transport FACH and PCH are organized. Depending on network configuration, these transport channels can use the same physical channel SCCPCH or can be configured, for each transport channels is assigned a physical channel SCCPCH. Expansion coefficient of the spectrum in the channel SCCPCH is permanent. The method of channel coding SCCPCH uses a convolutional code with half the speed (rate 1 / 2). To send data via FACH can also be used turbo or convolutional coding at 1/3 rate. SCCPCH does not contain information about power management. Figure. 4. The structure of the frame SCCPCH channel Fig. 4 shows SCCPCH structure. The frame consists of 15 slots, FACH or PCH is transmitted in each slot. The length of each slot consists of 2560 chips, the number of transmitted bits depends on the coefficient of expansion (rate) [3, 4]. Main time parameters of the system are determined by a standard that is easy to calculate. Based on the fact that the duration of the frame Тfr=10 мс, one frame transmits 15 time slots, the duration of one slot is Т sl = Т fr / 5 = 10 х 10-3 s / 15 == 0,667 ms. One slot transmits N ch = 2560 chips, the duration of one chip equals. Тch= Тsl/ Nch = 0,667 ms/2560 = 0,26 ms.

5 In the downlink SF(Spreading Factor) is from 4 to 512 (4, 8, 16, 32, 64, 128, 256, 512) [5]. Transfer process in the UMTS system is more complicated than in GSM, but the basic procedures in forming the output signal is similar. Main stages of signal formation shown in Fig. 5. Figure. 5. The radio signal formation 1. User data is added to the check sequence - CRC. 2. Data is divided into blocks. Length of the blocks Z may be different depending on the regime. (Normal Z = 504 bits, turbo mode Z = 5114 bits mode when segmentation is not used). 3. Channel coding is used as a method of protecting information against the distortions and errors in the transmission through the radio. Channel coding can be of several types: 3.1. When encoding 1 / 2: Y = 2K +16 (where, Y - the number of bits after encoding, K - number of bits at the input of the encoder) When coding 1 / 3: Y = 3K With turbo coding 1 / 3: Y = 3K Do not use channel coding Y = K. 4. Matching rates of logical channels (if necessary). 5. Insert the first indicator for the determination of DTX segments belonging to the same post. 6. The first interleaving - is still one of the methods to protect against biases and errors. 7. Segmentation of the radio frame. 8. Insert the second indicator DTX. 9. Segmentation for the imposition of a physical channel. 10. Second interleaving. 11. Overlay on a physical channel.

6 12. Spread spectrum. 13. Scrambling. 14. Modulation [5, 8]. Characteristics of GSM and WCDMA networks are listed in Table 1. WCDMA is better not only with the basic parameters of the radio interfaces, but especially for the broadcast mode (CellBroadcast) (see table cell with the selected text). Table 1. The main characteristics of the WCDMA and GSM radio interface Conclusion The analysis of the formation WCDMA networks compared to GSM networks is given. Broadcast chanels (WPC) are chosen, taking into account their (STSN, FACH, SCCPCH, PCH, SDCCH) interaction with the channels used for other purposes (personal data transmission and control). Speed limit and amount of transmitted data is given for such broadcast, which allows us to characterize the real possibilities of using WCDMA and GSM networks to organize mass service for public notification. References 1. 3GPP TS Technical Specification Group GSM /MML/3g/WCDMA3. 3. Technical Specification Group Radio Access Network; Radio interface for broadcast/multicast services. 3GPP TR UMTS/WCDMA Advanced overview. Adam Girycki. ENKI Gromakov YU.A. Standarty i sistemy podvizhnoy radiosvyazi. M.:EkoTrendz, p. 7. Tulyakov Yu.M., Abdalov V.V., Sorokina Ye.V. Obobshchennaya otsenka peredachi dannyh v sistemah podvizhnoy nazemnoy svyazi. M:. "Elektrosvyaz", 1, 2009 g. 8. Shloma A.M., Bakulin M.G., Kryeyndelin V.B., Shumov A.P. Novye tehnologii v sistemah mobilnoy radiosvyazi. M.: 2005 g.

7 9. Tulyakov YU.M., Shakarov D.Ye., Lashkin G.L. Osobennosti peredachi dannyh v sistemah podvizhnoy nazemnoy svyazi obshchego polzovaniya i ih statistika. Tezisy Mezhdunarodnaya nauchno-prakticheskaya konferentsiya "Telekom 2007", Rostov na Donu 2007 g.