WO2001019103A1

WO2001019103A1 - Method for overlaying packet-switched data services on a wireless network

Info

Publication number: WO2001019103A1
Application number: PCT/IB2000/001231
Authority: WO
Inventors: Peter A. Barany; Eric N. Johnson
Original assignee: Nortel Networks Limited
Priority date: 1999-09-03
Filing date: 2000-09-01
Publication date: 2001-03-15
Also published as: AU6717300A

Abstract

A mobile telecommunication system including a controller adapted to define a plurality of carriers for control and traffic signals in a packet network. There is also disclosed a method for allocating and reusing packet-switched channels to cells in a compact spectrum segment associated with a circuit-switched network. The packet-switched links are independent from the circuit-switched links.

Description

TITLE METHOD FOR OVERLAYING PACKET-SWITCHED DATA SERVICES ON A WIRELESS NETWORK

BACKGROUND

The invention relates to deploying packet-switched data services over a wireless network. Mobile communications systems, such as cellular or personal communications services (PCS) systems, are made up of a plurality of cells. Each cell provides a radio communications center in which a mobile unit establishes a call with another mobile unit or a wireline unit connected to a public switched telephone network (PSTN). Each cell includes a radio base station, with each base station connected to a mobile switching center that controls processing of calls between or among mobile units or mobile units and PSTN units.

From the original advanced mobile phone system (AMPS) standard, additional wireless protocols have been developed and implemented. One such protocol is the time- division multiple access (TDMA) protocol, originally implemented as the IS-54 standard (EIA/TIA/IS-54) and later followed by the IS-136 standard (TIA/EIA-136) from the Telecommunications Industry Association (TIA). With IS-136 TDMA, each channel carries a frame that is divided into six time slots to support up to three or six mobile units per channel. Other TDMA-based systems include Global System for Mobile (GSM) communications systems, which use a TDMA frame divided into eight time slots (or burst periods). Traditional speech-oriented wireless systems, such as the IS-136 and GSM TDMA systems, utilize circuit-switched connection paths in which a line is occupied for the duration of the connection between a mobile unit and the mobile switching center. Such a connection is optimum for communications that are relatively continuous, such as speech. However, data networks such as local area networks (LANs), wide area networks (WANs), and the Internet use packet-switched connections, in which communication between nodes on a communications link is by data packets. Each node occupies the communications link only for as long as the node needs to send or receive data packets. With the rapid increase in the number of cellular subscribers in conjunction with the rising popularity of communications over data networks such as intranets or the Internet, a packet-switched wireless data connection that provides access to the data networks, electronic mail, files in databases, and other types of data has become increasingly desirable.

Several packet-based wireless connection protocols have been proposed to provide more efficient connections between a mobile unit and a data network. One such protocol is the General Packet Radio Service (GPRS) protocol, which complements existing GSM systems. Another technology that builds upon GPRS that has been proposed is the Enhanced Data Rate for Global Evolution (EDGE) technology, which offers relatively high data rates and complements both GSM and IS-136 TDMA systems.

Because of frequency spectrum limitations, the number of channels that may be allocated for such packet-switched data services in a mobile communications system may be limited in some instances. For some service providers, allocating a relatively large bandwidth for packet-switched data services may mean that the spectrum for circuit-switched services may have to be reduced. On the other hand, for other service providers who are not spectrally challenged, a larger spectrum may be allocated for packet-switched data services. As a result, different systems may be implemented with different allocations of frequency spectrum for packet-switched services. Such systems may be incompatible with each other or with an underlying circuit-switched system. A need thus exists for a method and system for deploying packet-switched services that are compatible with existing systems.

SUMMARY

In general, according to one embodiment, an apparatus for use in a mobile communications system having a circuit-switched component providing a circuit-switched network and a packet-switched component providing a packet-switched network includes interface units adapted to communicate control signaling and traffic signaling over the circuit-switched and packet-switched networks. A system controller is adapted to define a plurality of carriers for communicating control and traffic signaling in the packet-switched network, and the system controller defines a protocol to communicate control signaling that is independent of control signaling in the circuit-switched network.

Some embodiments of the invention may offer one or more of the following advantages. The packet-switched component may be a stand-alone system that may be implemented without the need for an underlying circuit-switched system (e.g., a GSM system). Thus, a special beacon (such as the BCCH beacon of a GSM system) is not needed for the packet- switched component. The packet-switched network can be implemented with a compact spectrum (having relatively few carriers) or with an enhanced spectrum (having a larger number of carriers than the compact spectrum network). A packet-switched network having increased spectrum offers greater bandwidth. With a greater number of carriers, a higher channel reuse pattern may be employed for reduced interference. Other features and advantages will become apparent from the following description and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates an embodiment of a mobile communications system that provides both circuit-switched traffic links and packet-switched data links.

Figs. 2A-2B illustrate different arrangements of a compact spectrum system and an enhanced spectrum system in accordance with some embodiments for controlling communications over the packet-switched data links.

Figs. 3A and 3B illustrate carriers for use in the compact spectrum system and enhanced spectrum system, respectively, of Fig. 2 A or 2B.

Fig. 4 illustrates a 1/3 channel reuse pattern for packet data traffic communicated over packet-switched data links in the compact spectrum system of Fig. 2A or 2B.

Figs. 5 and 6 illustrate effective 4/12 and 3/9 channel reuse patterns in accordance with some embodiments that may be employed by the compact spectrum system of Fig. 2A or 2B.

Figs. 7-9 illustrate time-division multiple access (TDMA) frames for carrying control and traffic signaling in accordance with some embodiments in the compact spectrum system of Fig. 2A or 2B.

Fig. 10 illustrates a 52-frame multiframe for carrying control and traffic signaling in the compact spectrum system of Fig. 2A or 2B.

Figs. 11A, 1 IB, 12A and 12B illustrate multiframes in several time groups in accordance with some embodiments for carrying control and traffic signaling in the compact spectrum system of Fig. 2 A or 2B.

Fig. 13 illustrates a synchronization burst for use in either the compact spectrum or enhanced spectrum system of Fig. 2 A or 2B.

Fig. 14 illustrates an actual 4/12 channel reuse pattern for use in the enhanced spectrum system according to one embodiment. Fig. 15 illustrates an actual 4/12 channel reuse pattern for communicating control and traffic signaling in addition to a 1/3 channel reuse pattern for communicating traffic signaling in the enhanced spectrum system according to another embodiment.

Fig. 16 illustrates a TDMA frame structure for carrying control and traffic signaling in the enhanced spectrum system of Fig. 2A or 2B.

Fig. 17 illustrates a 52-frame multiframe structure, with a rotate feature disabled, for carrying control and traffic signaling in the enhanced spectrum system of Fig. 2A or 2B.

Fig. 18 illustrates a 52-frame multiframe structure, with a rotate feature enabled, for carrying control and traffic signaling in the enhanced spectrum system of Fig. 2A or 2B. Fig. 19 illustrates TDMA frames for carrying control and traffic signaling in transmit and receive paths of the packet-switched data link.

Fig. 20 is a block diagram of components in a mobile switching center (MSC), a base station, a data traffic service node, and a mobile unit in the mobile communications system of Fig. 1, with the data traffic service node adaptable to provide either the compact spectrum system or enhanced spectrum system of Fig. 2 A or 2B.

DETAILED DESCRIPTION In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.

Referring to Fig. 1, a mobile communications system 10, which may be a cellular or a personal communications services (PCS) system, includes a plurality of cells 14 each including a base station 18. The base station 18 is capable of communicating with mobile units 20 (e.g., mobile telephones, mobile computers, or other types of mobile units) over radio frequency (RF) wireless links. The base stations 18 are controlled by a mobile switching center (MSC) 12 for circuit-switched communications. For packet-switched or message-switched communications, the base stations 18 are controlled by a data traffic service node 35. In further embodiments, groups of base stations 18 may be controlled by base station controllers (not shown) that are in turn in communication with the MSC 12 and the data traffic service node 35.

In one embodiment, the base station 18 and mobile units 20 in each cell 14 are capable of communicating with two sets of carriers— a first set of carriers 26 for communicating circuit-switched traffic (e.g., speech data, short messaging services, and other circuit-switched data) and associated control signals; and a second set of carriers 28 or 328 for communicating packet-switched data traffic and associated control signals. In a further embodiment, packet-switched data traffic services may be provided without circuit-switched traffic services. As used here, circuit-switched traffic is referred to as primary traffic and packet-switched data traffic is referred to as packet data traffic. Packet data traffic may refer to any traffic that is sent in bursts of messages, packets, or other data structures over a link.

The packet data traffic services provided in the system 10 may be complementary to the primary traffic services offered by a conventional circuit-switched system, such as a time- division multiple access (TDMA) system according to the IS-136 protocol (TIA/EIA-136 from Telecommunications Industry Association). Alternatively, the primary traffic system may be part of a Global System for Mobile (GSM) communications system. The packet data traffic services in one embodiment may be according to the 136 high speed (136 HS) protocol as adopted by the Universal Wireless Communication Consortium (UWCC). The 136 HS protocol (also referred to as EDGE Compact or EGPRS Compact) incorporates much of the Enhanced Data Rate for Global Evolution (EDGE) technology adopted by ETSI (European Telecommunications Standards Institute).

In one embodiment, a compact spectrum system provides packet data services in a reduced frequency spectrum, e.g., less than about 1 megahertz (MHz) of spectrum. In another embodiment, an enhanced spectrum system provides packet data services in a larger spectrum, e.g., 2.4 MHz or more plus guard bands. A wireless network may include both compact and enhanced spectrum systems. In a compact spectrum system, the number of carriers employed for packet data services may be limited (e.g., 3 carriers in one embodiment). A larger number (e.g., 12) of carriers may be employed with the enhanced spectrum system.

A channel reuse plan in a compact spectrum system that employs a small number of channels may cause interference problems due to relatively small distances between cells or cell sectors having the same frequency. In accordance with some embodiments, a higher effective channel reuse plan is created by assigning cells or cell sectors to different combinations of frequencies and time. As a result, a higher effective channel reuse pattern (e.g., 3/9, 4/12, 7/21, etc.) that is based on both frequency and time can be achieved as compared to a reuse plan based only on the available frequencies, such as performed in conventional mobile systems. However, in the enhanced spectrum system, with the larger number of carriers that are provided, a higher actual channel reuse pattern (e.g., 3/9, 4/12, 7/21, etc.) that is based on frequencies may be employed.

In accordance with some embodiments of the invention, a mobile unit can be compatibly used in both the compact spectrum system and enhanced spectrum system. For example, referring to Fig. 2A, a wireless network including a plurality of cells (or cell segments) may include a first set that is part of a compact spectrum system 300 and a second set that is part of an enhanced spectrum system 302. As used here, a cell segment can refer to the entire cell, a cell sector, or some portion of a cell. Referring to Fig. 2B, a different arrangement of the enhanced spectrum system 302 is illustrated. In the Fig. 2B arrangement, the carriers F1-F3 (for carrying traffic, for example) are overlaid or underlaid with respect to the carriers A1-A3, B1-B3, C1-C3, and D1-D3 of the enhanced spectrum system. In other words, carriers F1-F3 and A1-A3, B1-B3, C1-C3, and D1-D3 may occupy the same geographic area in this arrangement. In other embodiments, a network of cells may include compact spectrum systems but not enhanced spectrum systems and vice versa. A mobile unit when crossing a boundary from an enhanced spectrum system to a compact spectrum system, or vice versa, communicates control and traffic signaling according to the procedure used in each of the systems. In accordance with some embodiments, the mobile unit may not even need to be aware that it has moved into a different system. The change in communications procedure may include different frequencies used to communicate signaling, the use of one time group in the enhanced spectrum system versus multiple time groups in the compact spectrum system, and other procedures as explained further below. By allowing a mobile unit to seamlessly transition between the systems, roaming of the mobile unit between the systems is facilitated.

Referring further to Figs. 3A and 3B, according to some embodiments, the base stations 18 include transceivers 25 that send and receive 30-kHz (kilohertz) carriers (26) to carry circuit-switched traffic and associated control signals, e.g., according to the IS-136 protocol. In addition, in a compact spectrum system (Fig. 3A), packet data traffic (e.g., packet-switched data) and associated control signals are carried by three 200-kHz carriers (28), FI, F2, and F3, that may be provided by transceivers 27 in each base station 18 in the same cell as the 30-kHz carriers. Guard bands 30 are defined between the first set of carriers 26 and the second set of carriers 28. The second set of three 200-kHz carriers 28 and guard bands 30 may be deployed in less than approximately 1 MHz of frequency spectrum.

In an enhanced spectrum system (Fig. 3B), packet data traffic and associated control signals are carried by twelve 200-kHz carriers 328 with guard bands 330 deployed between the carriers 328 and primary carriers 26. These twelve carriers 328 are referred to as Al, A2,

A3, Bl, B2, B3, Cl, C2, C3, Dl, D2, and D3. Additional carriers may be included in the enhanced spectrum system to further increase capacity.

The MSC 12 includes a primary traffic system controller 42 that controls the establishment, processing, and termination of circuit-switched calls (e.g., speech, short messages, and so forth) between or among mobile units 20 in one or more cells 14 or between or among mobile units 20 in a cell 14 and a wireline device (e.g., a telephone) coupled to a public switched telephone network (PSTN) 16. More than one MSC (such as an MSC 34 associated with a different service provider) may be included in the mobile communications system 10. The data traffic service node 35 includes a data traffic system controller 40 that controls the establishment, processing, and termination of packet-switched communications. In one embodiment, the data traffic service node 35 may be a serving GPRS support node (SGSN) according to the General Packet Radio Service (GPRS) protocol. Also in accordance with GPRS, the SGSN 35 communicates with a gateway GPRS support node (GGSN) 36, which provides an interface to a data network 32. Example data networks 32 include local area networks (LANs), wide area networks (WANs), the Internet, or other types of private or public networks. Communications across data networks may proceed according to TCP/IP (Transmission Control Protocol/Internet Protocol). More generically, the nodes 35 and 36 may include any system or systems that are capable of controlling packet-switched data communications between a mobile unit 20 and the data network 32. Further, the nodes 35 and 36 may be implemented in the same platform as the MSC 12 in an alternative embodiment.

Effectively, two wireless links are provided for mobile units 20 in the cells 14 controlled by the MSC 12: a packet data link, including the carriers 28 or 328, the base stations 18, and the data traffic system controller 40, to provide relatively high-speed (up to 384 kbps or higher, for example) packet-switched communications between mobile units 20 and the data network 32; and a primary traffic link, including the carriers 26, the base stations 18, and the primary traffic system controller 42 to provide speech and other circuit- switched communications between mobile units 20 or between a mobile unit 20 and a PSTN unit. In alternative embodiments, the packet data link may be implemented without the primary traffic link.

In one example embodiment, the primary traffic system controller 42 controls communications according to the IS-136 protocol. In another example, the primary traffic system controller 42 may control communications according to the GSM protocol, which uses 200-kHz carriers, instead of 30-kHz carriers, to carry primary traffic. In the primary traffic link, TDMA frames may be used to carry traffic and control signals. A frame according to IS-136 includes six time slots, while a frame according to GSM includes eight time slots. In the packet data link, frames are also defined to carry data traffic and associated control signals. The frame for the packet data link may be similar to a GSM frame with eight time slots (also referred to as burst periods) TN0-TN7 (described further below in connection with Figs. 7-9).

In the illustrated embodiment, the data traffic system controller 40 and the primary traffic system controller 42 (implementable with software or a combination of software and hardware) may be implemented in separate platforms (the data traffic service node 35 and the MSC 12, respectively). In an alternative embodiment, the system controllers 40 and 42 may be implemented in the same platform. Similarly, transceivers for sending and receiving carriers 26 and 28 or 328 may be included in the same base station 18 or in separate base stations.

In one arrangement, each cell may be divided into three sectors. The primary traffic link may utilize a 7/21 channel reuse pattern. The frequency reuse distance D for a 7/21 channel reuse pattern is large enough such that the C/I (carrier-to-interference) performance of control channels on the primary traffic link is robust. With the packet data link in a compact spectrum system, however, each base station site is allocated three frequencies FI, F2, and F3 (see also Fig. 3 A), one per sector, using a 1/3 frequency reuse pattern for data traffic, as illustrated in the tricellular representation of Fig. 4. As is generally known in the art, an equivalent trisector representation may also be used to show the cellular arrangement of Fig. 4. One frequency Fx is allocated per sector of each cell 14. Data traffic in the packet data link may employ various mechanisms, including link adaptation and incremental redundancy, to provide more robust C/I performance in a 1/3 channel reuse pattern. However, for control signals in the packet data link, the 1/3 channel reuse pattern is vulnerable to interference because the same frequencies are reused within relatively small distances of each other. To provide more robust C/I performance, a higher effective channel reuse pattern, e.g., 3/9, 4/12, and other patterns, may be employed in accordance with some embodiments. This is made possible by creating time groups so that control channels may be staggered in time to create the higher effective channel reuse pattern. With the packet data link in the enhanced spectrum system, an actual 3/9 or 4/12 channel reuse pattern may be employed instead of the effective 3/9 or 4/12 channel reuse pattern in a compact spectrum system. This is accomplished by eliminating the multiple time groups (in one configuration of the enhanced spectrum system) and increasing the number of carriers from 3 to 12. In another configuration of the enhanced spectrum system, however, multiple time groups (e.g., 3 or 4) and multiple carriers (e.g., 12) may be employed.

Figs. 5-12 below discuss communications of control signaling in a compact spectrum system. Figs. 14-18 below discuss communications of control signaling in an enhanced spectrum system.

Referring to Fig. 5, an effective 4/12 channel reuse pattern of a compact spectrum system is illustrated. In the effective 4/12 pattern, four time groups (T1-T4) are created. Thus, in addition to a reuse pattern based on the three frequencies F1-F3, the reuse pattern also has an orthogonal aspect based on time (T1-T4). Thus, each sector is assigned a frequency Fx as well as a time group Ty. With three frequencies FI, F2, and F3 and four time groups Tl, T2, T3, and T4, a cluster 100 of 12 sectors can be defined. The cluster 100 is then repeated to provide the effective 4/12 channel reuse pattern. In effect, time reuse that is added on top of frequency reuse creates a higher effective channel reuse pattern for control channels on the packet data link, thereby creating more robust performance with reduced interference problems.

As illustrated in Fig. 5, a sector having a certain frequency Fx in time group Ty is separated by some distance from another sector having the same frequency Fx and being in the same time group Ty (generally the distance provided by the width and length of each cluster 100). For example, the sectors 102 having frequency FI and belonging to time group T4 are separated by relatively large distances from each other to reduce the likelihood of interference. Another advantage offered by the effective 4/12 channel reuse pattern as illustrated in

Fig. 5 is that adjacent channel interference is reduced between the FI and F2 carriers and the F2 and F3 carriers. For any given sector having frequency Fx and assigned time group Ty, no adjacent sector is assigned the same time group Ty. For example, the sector 102 is associated with FI and T4. The sectors adjacent the sector 102 are in one of time groups TITS but not T4. Since adjacent sectors are communicating control channels in different time periods, interference between adjacent carriers (FI, F2, F3) is reduced. As a result, guard bands do not need to be defined between the carriers FI, F2, and F3, which allows for reduced frequency spectrum allocation for carriers used to communicate packet data.

Referring to Fig. 6, an effective 3/9 reuse pattern of a compact spectrum system is illustrated. The effective 3/9 reuse pattern utilizes three time group Tl, T2 and T3. This effectively provides a cluster 101 of nine sectors in which each sector has a distinct combination of a frequency Fx and time group Ty. With the effective 3/9 reuse pattern, the reduced adjacent channel interference feature as offered by the effective 4/12 reuse pattern is not available. To reduce interference between adjacent carriers FI, F2, and F3, guard bands between the carriers may need to be defined.

More generally, the packet data link may employ a 1/N channel reuse pattern based on N channel frequencies that may be allocated among N cell sectors. To provide a higher effective channel reuse pattern, M time groups can be defined to provide an effective M/(M*N) channel reuse pattern, provided a sufficient number of time slots are contained in frames to provide the M time groups. Alternatively, instead of one frequency per cell sector, the N channel frequencies may be divided into groups of two or more with a group allocated to each sector. Such techniques to provide higher effective channel reuse patterns may be employed also with non-sectored cells. Thus, cell segments in each cluster are allocated different combinations of frequencies and time groups.

To enable the creation of time groups so that they can be allocated among sectors of each cluster (100 or 101) to provide higher effective channel reuse, the base stations 18 are time synchronized with each other. This may be performed by using a global positioning system (GPS) timing receiver or some other synchronization circuit 19 (Fig. 1) in each base station 18. Synchronization of the base station 18 is employed to ensure alignment of the time groups in the cell sectors. Base station synchronization is carried out such that the following two criteria are satisfied. TDMA frames (including time slots TN0-TN7) of the packet data link are aligned with each other in all sectors. Thus, time slot TNO occurs at the same time at each base station site in each sector, to within tolerances of the synchronization equipment and any differences in propagation delays. Further, according to one embodiment, the control and traffic channels of the data link are carried by a multiframe structure (discussed further below in connection with Figs. 10-12). Each multiframe structure starts with frame 0 and continues to frame NN (e.g., 50 or 51). When time synchronized, frame 0 occurs at the same time in each sector.

The channels employed in the packet data link include packet broadcast control channels (PBCCH), packet common control channels (PCCCH), and packet data traffic channels (PDTCH). The broadcast control channels PBCCH, communicated downlink (from base station to mobile unit), provide general information on a per base station basis (e.g., cell/sector specific information) including information employed for mobile units 20 to register in the system 10. The common control channels PCCCH carry signaling information used for access management tasks (e.g., allocation of dedicated control channels and traffic channels). PCCCH includes a packet paging channel (PPCH) and a packet access grant channel (PAGCH) for downlink communications, and PCCCH includes a packet random access channel (PRACH) for uplink communications (mobile unit to base station). PRACH is used by a mobile unit 20 to request access to the system 10. PPCH is used by the base station 18 to alert a mobile unit 20 of an incoming call. PAGCH is used to allocate a channel to a mobile unit 20 for signaling to obtain a dedicated channel following a request by the mobile unit 20 on PRACH. Other control channels include a packet frequency correction channel (PFCCH) and a packet synchronization channel (PSCH). PFCCH and PSCH are used to synchronize a mobile unit 20 to the time slot structure of each cell by defining the boundaries of burst periods and time slot numbering. In one embodiment, the control channels discussed above are extensions of circuit-switched logical channels used in a GSM system. Referring to Fig. 13, a PSCH burst is illustrated. In one embodiment, the PSCH burst is 148 bits long plus a guard period (GP) of 8.25 bits (symbols). The PFCCH burst also has the same length as the PSCH burst and is also associated with a guard period of 8.25 bits.

The control channels that are communicated with the higher effective 3/9, 4/12, or other channel reuse pattern include PBCCH, PCCCH, PFCCH, and PSCH. The data traffic channels PDTCH and associated traffic control channels, PTCCH (packet timing advance control channel) and PACCH (packet associated control channels) use the 1/3 reuse pattern, since traffic channels employ various mechanisms, as noted above, to better withstand interference from neighboring cell segments. Referring to Fig. 7, each carrier (FI, F2 or F3) in the packet data link of a compact spectrum system carries a TDMA frame 110 that is divided into a plurality of time slots. In the illustrated embodiment, eight time slots (or burst periods) TN0-TN7 are used. However, in further embodiments, a carrier may be divided into a smaller or larger number of time slots. In one embodiment, each TDMA frame 110 is structured like a GSM frame and has a length of 120/26 ms (or about 4.615 ms). To provide an effective 4/12 reuse pattern, control channels are staggered across four different time groups. In the illustrated embodiment, in time group 1, control channels (PBCCH, PCCCH, PFCCH, and PSCH in one embodiment) are transmitted during time slot TNI; in time group 2, control channels are transmitted in time slot TN3; in time group 3, control channels are transmitted during time slot TN5; and in time group 4, control channels are transmitted during time slot TN7. By staggering the control channels into different time slots as illustrated, a channel reuse pattern may be divided according to both frequency and time. As illustrated in Fig. 7, the time slots are marked as one of a T time slot (during which packet data traffic may be communicated), a C time slot (during which control signals may be communicated), and an I time slot (during which all traffic and control channels may be idle in blocks that transmit PBCCH and PCCCH on other time groups but which transmit packet data traffic otherwise, as explained below in connection with Figs. 11 and 12). In one embodiment, a block includes four frames of a multiframe (e.g., a 51- or 52-frame multiframe).

Referring to Fig. 8, an effective 3/9 reuse pattern includes three time groups Tl, T2 and T3. In the illustrated embodiment, the control channels are placed in time slot TNI (in time group Tl), time slot TN3 (in time group T2), and time slot TN5 (in time group T3). The time slots that carry control channels are indicated as being C time slots. Also illustrated in Fig. 8 are T time slots (during which packet data traffic may be transmitted) and I time slots (which are idle during blocks that transmit PBCCH or PCCCH in other time groups but which carry packet data traffic otherwise).

In further embodiments, the control channels may be carried in time slots other than TNI, TN3, TN5 or TN7 (Fig. 7) or TNI, TN3, or TN5 (Fig. 8). For example, instead of placing control channels in odd time slots TNI, 3, 5 and 7, the control channels may be placed in time slots TNO, TN2, TN4, and TN6 in the different time groups. Other staggering schemes may also be employed, with some control channels communicated in even time slots and others communicated in odd time slots, for example. Referring to the example of Fig. 9, which shows a 3/9 reuse pattern, control channels may be placed in the C time slots: time slot TNO in time group 1, time slot TN2 in time group 2, and time slot TN4 in time group 3. The T time slots carry data traffic, and the I time slots are idle during blocks that transmit PBCCH or PCCCH in other time groups but carry packet data traffic otherwise. With larger or smaller numbers of time slots, other staggering schemes can be provided to provide fewer or larger numbers of time groups.

Referring to Figs. 10-12, communication using 52-frame multiframes 120A and 120B in accordance with some embodiments is illustrated. The structure of a multiframe 120 is illustrated in Fig. 10. Each multiframe 120 includes 52 TDMA frames (FRN 0-51), which are divided into 12 blocks B0-B11, leaving four frames FRN 12, 25, 38, and 51 to carry predetermined channels. In further embodiments, other multiframe structures may be used, such as a 51 -frame multiframe. For each time group (1, 2, 3, or 4), the eight columns of the multiframe 120 correspond to the eight time slots TN0-TN7, and the 52 rows correspond to the 52 frames of the multiframe 120. Figs. 11A and 1 IB illustrate a multiframe structure 120 A employing an effective 4/12 reuse pattern, and Figs. 12A and 12B illustrate a multiframe structure 120B employing an effective 3/9 reuse pattern.

In the illustrated example of Figs. 11 A, 1 IB, 12A and 12B, three blocks are assigned to PCCCH (frames containing a C) and one block is assigned to PBCCH (frames containing a B). A block includes four TDMA frames. The number of blocks allocated for PBCCH and PCCCH is flexible, from two up to 12 blocks per time slot in each multiframe 120. In the illustrated examples, PBCCH is carried in block B0, and PCCCH is carried in blocks B5, B8, and Bl 1. Frames FRN 25 and 51 carry PFCCH and PSCH, respectively, and frames FRN 12 and 38 carry PTCCH. Frames marked with an "X" are idle, and correspond to the odd time slots (TNI, TN3,

TN5, or TN7) in blocks (0, 5, 8, and 1 1) that carry control channels PBCCH and PCCCH in other time groups. Thus, for example, the frames in block B0 in time slot TN3 in each of time groups 1, 3, and 4 are idle because the frames in time slot TN3 of time group 2 carries PBCCH. The same is true also for frames in blocks B5, B8, and Bl 1 in time slots TNI, 3, 5, or 7 that do not carry control signaling.

By using the channel reuse pattern in accordance with some embodiments in which channel reuse is based both on frequency and time, it is possible to reduce the spectrum that is allocated to carriers for the packet data link. In the described embodiment, the allocated spectrum can be maintained below about 1 MHz by using three 200-kHz carriers (600 kHz) and a guard band. Although the basic channel reuse pattern is 1/3 for packet data traffic in the described embodiment, higher effective reuse patterns (3/9, 4/12, or other) are provided for the control channels to reduce the likelihood that interference will cause failures of wireless communication. Consequently, a wireless packet data link that complements (or overlays) an existing wireless primary traffic link may be allocated a reduced frequency spectrum while using an aggressive channel reuse pattern for data (or bearer) traffic. By limiting the frequency spectrum that needs to be allocated for the packet data link, displacement of existing primary traffic can be avoided. Such displacement may occur if a conventional frequency reuse plan of 3/9, 4/12, or 7/21 is used.

To extend the spectrum available for packet-switched services in accordance with some embodiments, a compact spectrum system may be modified to provide the enhanced spectrum system. This allows the enhanced spectrum system to be backwards compatible with the compact spectrum system. Further, both the compact spectrum and enhanced spectrum systems are "stand-alone" systems in that each system does not require the existence of an underlying circuit-switched system (such as IS-136 or GSM) for operation. In other words, the enhanced spectrum system or compact spectrum system may be implemented as systems separate from and independent of circuit-switched systems to provide packet-switched data services. In a compact spectrum system, predetermined bits (referred to as TG bits) are used in the PSCH and PFCCH bursts to determine the time group that each sector is allocated to. Thus, the TG bits, which in one embodiment ranges in value from 0 to 3, may indicate in which of up to four time groups a cell sector may be allocated. Thus, in a compact spectrum system, the TG bits are employed for dividing a cluster of cell sectors into multiple time groups to provide the desired higher effective channel reuse pattern.

However, for one configuration of the enhanced spectrum system, only one time group is used along with 9, 12 or more separate carriers to achieve a higher actual channel reuse pattern (e.g., 3/9 or 4/12). More generally, given N carriers, an (N/3)/N channel reuse pattern of may be implemented. Any one of the time groups may be selected to carry control signaling in the enhanced spectrum system. Thus, for example, any one of time groups Tl, T2, T3, and T4 (corresponding to time slots TNI, TN3, TN5, and TN7) may be selected to carry control signaling. In further embodiments, other time slots may be assigned to the time groups. In addition, in yet other embodiments of the enhanced spectrum system, more than one time group may be employed. To reduce likelihood of interference with the measurement of control bursts for selection or re-selection, time groups T3 and T4 (corresponding to time slots TN5 and TN7) may be selected (in the embodiment in which only one time group is used) to carry control signaling in the enhanced spectrum system. In predetermined frames, a mobile unit measures the PSCH and PFCCH bursts of the cell sector it is in as well as in neighboring cell sectors to perform selection and re-selection, respectively, of a cell sector. Selection and re-selection are based on the strength of the PSCH and PFCCH bursts. Referring to Fig. 14, an actual 4/12 channel reuse pattern as employed in an enhanced spectrum system is illustrated. The 12 different frequencies are illustrated as Al, A2, A3, Bl, B2, B3, Cl, C2, C3, Dl, D2, and D3. In further embodiments, other reuse patterns may be employed, including 3/9 and other patterns. The 4/12 channel reuse pattern illustrated in Fig. 14 is employed to carry the control and traffic signaling of the enhanced spectrum system, including PFCCH, PSCH, PBCCH, PCCCH, PDTCH, PACCH, and PTCCH, which are identical to the control and traffic signaling employed in a compact spectrum system.

Referring to Fig. 16, time group T3 (corresponding to time slot TN5) has been selected to communicate control signaling (e.g., PFCCH, PSCH, PBCCH, PCCCH), with the remaining time slots TN0-TN4 and TN6-TN7 used for carrying traffic signaling (e.g., PDTCH, PACCH, PTCCH). Referring further to Fig. 17, a 52-frame multiframe 500 in accordance with one embodiment has 52 frames (FRN 0-51). In the illustrated embodiment, frames FRN 0-3 carry the broadcast channels PBCCH, frames FRN 21-24, 34-37, and 47-50 carry the common control channels PCCCH, frame 25 carries the frequency correction channel PFCCH, and frame 51 carries the synchronization channel PSCH, all in time slot TN5. In addition, frames 12 and 38 carry the packet timing advance control channel PTCCH. Except for the frames carrying PFCCH and PSCH, none of the other frames have to be defined as idle in the embodiment illustrated in Fig. 17. Thus, a distinct advantage offered by the enhanced spectrum system over a compact spectrum system (one embodiment illustrated in Figs. 11A, 1 IB, and 12) is that no idle slots are required other than the idle slots in the frames carrying PFCCH and PSCH. This increases the bandwidth available over the packet data link for packet-switched services. The higher bandwidth may allow real-time services such as live audio and multimedia communications and any other communications, which involves streaming of data.

In other embodiments of the enhanced spectrum system, multiple time groups may be employed to carry control signaling over carriers A1-A3, B1-B3, C1-C3, and D1-D3. For example, if three time groups (Tl, T2, and T3) are used, then carriers Al, A2, and A3 are communicated in time groups Tl, T2, and T3, respectively. Similarly, carriers Bl, B2, and B3 are communicated in time groups Tl, T2, and T3, respectively; carriers Cl, C2, and C3 are communicated in time groups Tl, T2, and T3, respectively; and carriers Dl, D2, and D3 are communicated in time groups Tl, T2, and T3, respectively. Other arrangements are also possible.

In one example in which four time groups (Tl, T2, T3, and T4) are employed, carriers

Al, A2, A3, and Bl may be communicated in time groups Tl, T2, T3, and T4, respectively; B2, B3, Cl, and C2 may be communicated in time groups Tl, T2, T3, and T4, respectively; and C3, Dl, D2, and D3 may be communicated in time groups Tl, T2, T3, and T4, respectively. In embodiments employing multiple time groups, time group rotation is enabled, as described further below.

Referring to Fig. 15, in another embodiment, an even larger spectrum of carriers may be allocated for the enhanced spectrum system. In the Fig. 15 embodiment, in addition to the

12 carriers A1-A3, B1-B3, C1-C3, and D1-D3 for carrying control signaling and traffic signaling, three additional carriers F1-F3 (which are the same carriers in the compact spectrum system) may be used to carry traffic signaling PDTCH, PACCH, and PTCCH. In this scheme, the carriers A1-A3, B1-B3, C1-C3, and D1-D3 employ an actual 4/12 channel reuse pattern to communicate control signaling and traffic signaling, while the carriers F1-F3 employ a 1/3 channel reuse pattern to communicate traffic signaling. This scheme offers added capacity over the scheme employed in Fig. 14.

As noted above, in the configuration of the enhanced spectrum system in which a singular time group is selected to carry control signaling, time group T3 or T4 may be selected to reduce the likelihood of interference in the measurement of the PSCH and PFCCH bursts to perform selection and re-selection, respectively, of a cell sector. This is explained in connection with Fig. 19 below.

Referring to Fig. 19, the receive (downlink) and transmit (uplink) paths in an enhanced spectrum system are illustrated. A measurement window is defined during which a mobile unit 20 can measure either PSCH (for cell sector selection) or PFCCH (for cell sector re-selection). The measurement window in this example is for a mobile unit that is active on time slot TNO. With other arrangements, the measurement window begins and ends at different time slots.

The time slots between the receive and transmit paths are out of phase by three time slots. If time group Tl is selected for control signaling, then time slot TNI may be the one used to carry PSCH or PFCCH. For time group Tl, the time slots TNO and TN2-TN7 are idle in frame FRN 25 (which carries PFCCH) and frame FRN 51 (which carries PSCH). Thus, during the measurement window, a first mobile unit can measure PSCH or PFCCH (on the downlink path) in time slot TNI (if time group Tl has been selected). However, during receipt of PSCH or PFCCH in TNI, a second mobile unit (in a neighboring cell sector) may be transmitting traffic in time slot TN6. Transmission of such traffic in TN6 by the second mobile unit may interfere with the measurement of PSCH or PFCCH by the first mobile unit. Similar interference may occur if time slots TNO, TN2, or TN3 are used to carry control signaling. By assigning time groups T3 or T4 (time slots TN5 or TN7) to carry control signaling, such interference may be avoided since frame 25 or 51 in the transmit path is idle. Other suitable time slots may also be employed for carrying control signaling, such as time slots TN4 and TN6. As a result, a mobile unit in a cell sector of the enhanced spectrum system will be able to more reliably measure PSCH and PFCCH bursts of all neighboring cell sectors.

However, if it is desired to use time slots TNI or TN3 (corresponding to time groups Tl or T3, respectively), or one of the other time slots TNO or TN2, then a time group rotation scheme may be employed. It is contemplated that time group rotation may be enabled regardless of the time slot selected. Further, if multiple time groups are selected, then time group rotation may be employed.

A time group rotation scheme is employed in some compact spectrum systems for addressing the interference between transmission of traffic and measurement of PSCH or PFCCH bursts. Time group rotation refers to the rotation of the time group assigned to each sector for carrying control signaling. Thus, for example, a given sector may rotate among time slots TN7, 5, 3, and 1. In a compact spectrum system, all sectors are rotated concurrently so that division of time groups among the sectors is maintained. Rotation may be accomplished by updating the value of TG with each new occurrence of a multiframe. In one embodiment of a compact spectrum system, the value of TG may be rotated with each increment of a predetermined parameter MFN, which represents the multiframe number that ranges between 0 and 3. MFN is calculated from the TDMA frame number FRN according to the following: MFN = (FRN div 52) mod 4. With each increment of MFN, the value of TG is rotated to rotate the time group assigned to each cell sector. In some compact spectrum systems, the time group rotation occurs between frame numbers (FRN) mod 52 equal to 3 and 4. By rotating the time group allocated to each sector, failure of a mobile unit in measuring PSCH or PFCCH during a predetermined measurement window in one time group can be remedied in one of the other time groups to which the sector will rotate too.

Time group rotation may be extended to some embodiments of an enhanced spectrum system if certain time slots are used to carry control signaling in a single time group scheme, such as time slots associated with time groups Tl and T2. In embodiments of the enhanced spectrum system that employ multiple time groups, time group rotation is also employed. In an enhanced spectrum system, rotation may be enabled by setting a predetermined parameter (referred to as ROTATE) in the PSCH burst to a predetermined value. For example, if ROTATE is set at 0, rotation may be enabled. On the other hand, if ROTATE is set at 1 , then rotation may be disabled.

Referring to Fig. 18, a multiframe 600 used by an enhanced spectrum system in which rotation has been activated is illustrated. As illustrated, time slot TN5 (for time group T3) is used for carrying the PBCCH channel. However, between frames FRN 3 and 4, the rotation of the value of TG occurs to cause the cell sector to transition to time group T2. Thus, further into the multiframe 600, time slot TN3 is used to carry the PCCCH channels. In the next multiframe 600, rotation from time group T2 to time group Tl occurs.

To avoid rotation and the associated complexities of rotation, an enhanced spectrum system can use one of time groups T3 or T4 in a single time group scheme. However, the enhanced spectrum system may also offer flexibility in using time group Tl or T2 (or multiple time groups) for carrying control signaling by having the ability to activate rotation.

Another feature that may be offered by some enhanced spectrum systems is the ability to use one of the carriers A1-A3, B1-B3, C1-C3, and D1-D3 as a beacon. Thus, referring to either Fig. 17 or 18, during periods in which traffic is idle, dummy bursts may be sent in time slots not carrying traffic.

Some embodiments of the invention may offer one or more of the following advantages. A packet-switched link having increased spectrum is provided for packet- switched data services. Such increased spectrum offers the ability of communicating realtime data, such as audio, multimedia, and other streaming data. An enhanced spectrum system offering the increased spectrum packet- switched link may be compatible with packet- switched wireless systems having a more compact spectrum to allow a mobile unit to roam between the different systems. In the enhanced spectrum system, a relatively high channel reuse pattern may be employed since more carriers are allocated. This in turn reduces the amount of idle time slots needed as compared to the time slots used in a system having a more compact spectrum. Reduction of time slots allows more time slots to carry traffic, thereby improving the overall bandwith of the network.

The enhanced spectrum system is a stand-alone system that may be implemented without the need for an underlying circuit-switched system (e.g., a GSM system). Thus, a special beacon (such as the BCCH beacon of a GSM system) is not needed for the enhanced spectrum system.

A further advantage is that a mobile unit is able to compatibly operate in either an enhanced spectrum system or a system having a more compact spectrum. This is achieved by using many of the same features and procedures, except for different carriers, elimination of multiple time groups in the enhanced spectrum system, and the ability to activate or deactivate rotation in the enhanced spectrum system. Thus, a mobile unit that travels from a cell sector in an enhanced spectrum system to a cell sector in a compact spectrum system, and vice versa, may not need to know that it has made such a transition. The control signaling communicated to and from the mobile unit is carried in a time group set by TG, which is carried in the PSCH burst. In an enhanced spectrum system, a single time group (rotated or not rotated) is used by all sectors. In a compact spectrum system, cell sectors may use multiple time groups. However, from the perspective of a mobile unit when it is in a cell sector of a compact spectrum system, only one time group TG (rotated) is used. The difference is that the mobile unit may detect different time groups used in neighboring cell sectors in a compact spectrum system, whereas the same time group is used in neighboring cell sectors of an enhanced spectrum system.

Referring to Fig. 20, components of the MSC 12, a base station 18, the data traffic service node 35, and a mobile unit 20 are illustrated. The data traffic service node 35 and base station 18 are configured differently depending on whether they are part of a compact spectrum system or an enhanced spectrum system. For example, more carriers are defined in the enhanced spectrum system, multiple time groups are not used in the enhanced spectrum system, and rotation can be selectively activated or deactivated in the enhanced spectrum system. In the base station 18, the primary traffic transceiver 25 and packet data traffic transceiver 27 are connected to an antenna tower 54 that transmits and receives the first and second sets of carriers 26 and 28. The primary traffic and packet data traffic transceivers 25 and 27 are connected to a controller 50, which may be implemented in hardware or a combination of hardware and software. Also connected to the controller 50 is a GPS timing receiver or other synchronization circuit 19 that allows synchronization of all base stations in the group of cells 14 controlled by the MSC 12 and data traffic service node 35. Further, the base station 18 includes an MSC interface 52 that is coupled to a link 64 (e.g., a Tl link) that is in turn coupled to an interface unit 56 in the MSC 12. The base station 18 also includes an interface 51 (which in one embodiment is a G_b interface 51 according to GPRS) for communicating over a link (e.g., a G_b link) to the data traffic service node 35.

In the MSC 12, a control unit 58 provides the processing core of the MSC 12. The control unit 58 may be implemented with computer systems, processors, and other control devices. The control unit 58 is connected to a storage unit 62, which may contain one or more machine-readable storage media to store various data as well as instructions of software routines or modules that are loadable for execution by the control unit 58. For example, instructions of routines or modules that make up the primary traffic system controller 42 may be stored in the storage unit 62 and loaded for execution by the control unit 58. The MSC 12 may also include a PSTN interface 60 that is coupled to the PSTN 16 to allow communications with a PSTN-connected unit. Further, the MSC 12 includes an interface 75 (e.g., a G_s interface) for communicating over a link (e.g., a G_s link) to the data traffic service node 35.

The data traffic service node 35 includes interface units 77 and 79 for communicating over the G_b and G_s links, respectively, in one embodiment. The processing core of the data traffic service node 35 includes a control unit 69, which may be implemented with computer systems, processors, or other control devices. A storage unit 71 including machine-readable storage media is coupled to the control unit 69. Instructions associated with the routines and modules that make up the data traffic system controller 40 may be initially stored in the storage unit 71 and loaded by the control unit 69 for execution. The data traffic service node 35 further includes an interface 81 (e.g., a G_n interface) for communicating with the GGSN 36 (Fig. 1). In another embodiment, the interface 81 may be a network interface controller or other transceiver capable of communicating over the data network 32. In further embodiments, the data traffic and primary traffic system controllers 40 and 42 may be implemented in one platform and executable by the same control unit. Carriers are communicated between the antennas 54 coupled to the base station 18 and an antenna 62 of a mobile unit 20. In one example arrangement of the mobile unit 20, one or more radio transceivers 64 are connected to the antenna 62 to send and receive packet data carriers and primary traffic carriers. A microprocessor 66 (or one or more other suitable control devices) may be coupled to the one or more radio transceivers 64. The microprocessor 66 is coupled to a storage unit 68, which may be in the form of a non-volatile memory (such as a flash memory or an electrically erasable and programmable read-only memory) and/or dynamic and static random access memories (DRAMs and SRAMs). Instructions of software routines 68 executable on the microprocessor 66 may be initially stored in a non- volatile portion of the storage unit 68. An input/output (I/O) controller 74 is coupled to the keyboard 70 and display 72 of the mobile unit 20.

The instructions of the software routines or modules may be loaded or transported into a system or device in one of many different ways. For example, code segments or instructions stored on floppy disks, CD or DVD media, the hard disk, or transported through a network interface card, modem, or other interface mechanism may be loaded into the system or device and executed as corresponding software routines or modules. In the loading or transport process, data signals that are embodied as carrier waves (transmitted over telephone lines, network lines, wireless links, cables, and the like) may communicate the code segments or instructions to the system or device. Such carrier waves may be in the form of electrical, optical, acoustical, electromagnetic, or other types of signals.

While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the invention.

Claims

What is claimed is: 1. A method for use in a mobile communications system, comprising providing a packet-switched link for communicating control and traffic signaling; defining a frame having a plurality of time slots; and assigning one of the time slots to communicate control signaling.

2. The method of claim 1, further comprising assigning a plurality of the time slots to communicate control signaling.

3. The method of claim 1, wherein the mobile communications system includes a plurality of cell segments, the method further comprising defining a channel reuse pattern for the cell segments.

4. The method of claim 3, wherein defining the channel reuse pattern includes defining a channel reuse pattern based on the number of carriers assigned to the packet- switched link.

5. The method of claim 4, further comprising assigning N carriers to the packet- switched link.

6. The method of claim 5, further comprising assigning at least one of the N carriers as a beacon channel.

7. The method of claim 5, wherein defining the channel reuse pattern includes defining an (N/3)/N channel ruse pattern.

8. The method of claim 1, further comprising selecting one of a plurality of time groups to carry control signaling, the selected one time group including the assigned one of the time slots.

9. The method of claim 1, further comprising selecting multiple time groups to carry control signaling, the selected time groups corresponding to multiple time slots of the frame.

10. The method of claim 9, further comprising rotating the time group to carry control signaling among the plurality of time groups.

11. The method of claim 10, further comprising assigning a predetermined field in a control burst as an indication of whether time group rotation is enabled or disabled.

12. The method of claim 11, wherein assigning the predetermined field includes assigning a bit in a synchronization burst.

13. The method of claim 1, wherein the mobile communications system includes a plurality of cells, the method further comprising synchronizing base stations in each of the cells.

14. The method of claim 1, further comprising providing a circuit-switched link to carry circuit-switched control and traffic signaling.

15. The method of claim 14, further comprising defining the packet-switched link to be independent of the circuit-switched link.

16. An apparatus for use in a mobile communications system having a plurality of cell segments, comprising: an interface unit adapted to communicate with the plurality of cell segments; and a system controller adapted to define a packet- switched link for use in the cell segments, the packet-switched link including a plurality of carriers for communicating control and traffic signaling in frames, each frame having a plurality of time slots, the system controller being adapted to select one or more of the time slots to communicate control signaling.

17. The apparatus of claim 16, wherein the same time slot is used in each cell segment to communicate control signaling.

18. The apparatus of claim 16, wherein different ones of a plurality of time slots are used in corresponding cell segments to communicate control signaling .

19. The apparatus of claim 16, wherein the packet-switched link includes N carriers, the system controller adapted to establish an (N/3)/N channel reuse pattern.

20. The apparatus of claim 16, wherein the system controller is adapted to communicate an indication of one of a plurality of time groups, each time group corresponding to a different one of the time slots.

21. The apparatus of claim 16, wherein the indication is part of a synchronization burst.

22. The apparatus of claim 16, wherein the system controller is adapted to update the indication to rotate the time group used to communicate control signaling.

23. The apparatus of claim 16, wherein the system controller is adapted to define at least one of the carriers as a beacon.

24. An apparatus for use in a mobile communications system having a circuit- switched component providing a circuit-switched network and a packet-switched component providing a packet-switched network, comprising: interface units adapted to communicate control signaling and traffic signaling over the circuit-switched and packet-switched networks; and a system controller adapted to define a plurality of carriers for communicating control and traffic signaling in the packet-switched network, the system controller defining a protocol to communicate control signaling that is independent of control signaling in the circuit-switched network.

25. A mobile communications system, comprising: a first system providing a first packet-switched wireless network; and a second system providing a second packet-switched wireless network, the first packet-switched wireless network having a first spectrum of carriers, and the second packet-switched wireless network having a second spectrum of carriers that is greater than the first spectrum, the first and second packet-switched wireless networks establishing communications procedures to allow a mobile unit to compatibly roam between the two networks.

26. An article including one or more machine-readable storage media containing instructions for controlling communications in a mobile communications system having a packet-switched network and a circuit-switched network, the instructions when executed causing a controller to: allocate a plurality of carriers for communicating control and traffic signaling in the packet-switched network; and define a protocol to communicate control signaling in the packet-switched network that is independent of control signaling in the circuit-switched network.

27. An apparatus for use in a mobile communications system having a plurality of cell segments, comprising: means for establishing wireless packet-switched communications in the plurality of cell segments; means for defining a plurality of carriers for communicating control and traffic signaling in frames, each frame having a plurality of time slots; and means for communicating control signaling in an assigned one or more of the time slots.