HK1175345B - Methods and apparatus for wireless network connectivity - Google Patents

Description

Method and apparatus for wireless network connectivity

This application is a divisional application of the patent application having application number 02815846.6 entitled "method and apparatus for wireless network connectivity", filed 2002, 08, 13.

RELATED APPLICATIONS

The present application claims priority from 60/312,126 of U.S. provisional patent application No. 8/14 of 2001, entitled "improved FOR PROVIDING network connectivity FOR A WIRELESS TERMINAL", the contents of which are incorporated herein by reference.

Technical Field

The present invention is directed to communication systems, and more particularly to methods and apparatus for supporting communication between a wireless terminal, such as a mobile node, and a plurality of base stations.

Background

In a wireless communication system, wireless terminals, such as mobile nodes, are often coupled to a wired network, such as the internet, through base stations. The base station provides network connectivity within the coverage area named cell. The communication path from the base station to the wireless terminal is called "downlink", and the communication path from the wireless terminal to the base station is called "uplink".

To achieve network connectivity, a wireless terminal communicates with at least one base station. However, for different performance factors that support terminal mobility, e.g., from cell to cell, a wireless terminal is typically equipped to maintain wireless link connections with multiple base stations simultaneously. For example, in a Code Division Multiple Access (CDMA) system, it is possible for a wireless terminal to be in a "soft handoff" state.

Fig. 1 illustrates a known CDMA communications network 100 that includes a wireless terminal 102, a base station 1104, a base station 2106, a mobile switching center 108, and a wireline network 110. Various communications between network elements are represented by arrows. Where uplink communication is depicted in fig. 1 and downlink communication is depicted in fig. 2.

In direct spread CDMA techniques, the existing soft handoff method is to deliver a single data information stream split among multiple link connections from different base stations, respectively, to a wireless terminal and to flow another data stream from the terminal to multiple base stations. The resulting characteristics include tight time synchronization of these connections between the base station and the terminal, and these characteristics constrain the technologies that can be chosen in the radio access network architecture.

Referring to fig. 1, in a soft handoff state, the wireless terminal 102 uses the uplink to transmit a signal 112, 114 representing the transmitted information. In this example, a wireless terminal 102 is within the coverage of more than one base station 104, 106. Thus, more than one base station 104, 106 will listen to the same uplink signal 112, 114 at the same time.

The base stations 104, 106 then process the received signals in response to receiving the signals 112, 114 from the wireless terminal 102. The results of the processing are transmitted, as indicated by arrows 116 and 118, to a central unit, generally referred to as a mobile switching center 108, which combines the results from the individual base stations 104,106 to obtain the transmitted information. The mobile switching center 108 then sends the information to a wired network 110, such as the internet. This operation is represented by arrow 120.

Also for the downlink depicted in fig. 2, the mobile switching center 108 receives information about the wireless terminal 102 from the wired network 110 as indicated by arrow 220. The mobile switching center 108 then copies the information and transmits it to more than one base station 104, 106, this operation is represented by arrows 216, 218. The base stations 104, 106 simultaneously transmit received signals representing the information to the wireless terminal 102. This operation is shown using arrows 212 and 214. The wireless terminal 102 combines the signals received from the base stations 104, 106 to obtain information from the wired network 110.

One advantage of having a soft handoff state is that macro diversity is achieved. In addition, soft handoff conditions also reduce data loss and latency in handoffs, i.e., when a wireless terminal is handed off from one base station to another, data is transmitted by multiple base stations.

Even when losing contact with a first base station, for example because of entering the coverage of a second base station, the data received by the wireless terminal from the first base station can be combined with the data received from a second wireless terminal transmitting the same signal to form a complete message or data set.

Soft handoff has a drawback associated with the complexity and timing requirements created by using the mobile switching center 108 as a combining unit in the uplink and a replicating unit in the downlink. This feature limits network operation since it requires the synchronous network transport technology to be able to deliver data to and from the mobile switching center 108 and the base stations 104, 106 with very low delay jitter relative to the multiple base stations 104, 106. That is, in such systems, information to and from the multiple base stations 104, 106 and the mobile switching center 108 must be closely synchronized in time. This synchronous network transport feature is in sharp contrast to packet switched data network operations that typically use asynchronous network transport techniques.

In mobile communication systems, maintaining multiple link connections simultaneously is important to ensure seamless handover. However, there are significant economic advantages to using more asynchronous forms of data networking technology within a radio access network. There is therefore a need for improved methods and apparatus for enabling wireless connectivity, at least some of which allow a wireless terminal to simultaneously connect to multiple base stations while enabling the base stations to communicate with a wired network in a manner consistent with asynchronous packet-switched data networking.

Disclosure of Invention

The present invention is directed to methods and apparatus that allow a wireless terminal to maintain connections with multiple base stations simultaneously.

The invention described herein allows a wireless terminal to be connected to multiple base stations, such as in an asynchronous network, simultaneously, yet still be able to transmit different data and/or control information streams in the respective link connections from each base station to the terminal and from the terminal back to the base stations. It follows that there may be simultaneous but different information flows between a wireless terminal and multiple base stations. For those base stations communicating with the terminal, no time synchronization is required between their link connections. There are therefore more technical options for use in radio access network architectures.

According to the invention, a plurality of simultaneous connections are subject to independent operation. Each connection may include an uplink, a downlink, or both. In the physical layer, a separate synchronization loop is tuned separately and used for each of the plurality of connections. To simplify the simultaneous operation of independent timing synchronization loops for supporting simultaneous communications with multiple base stations, multiple uplink and multiple downlink receivers and timing synchronization circuits may be included in each wireless terminal.

In higher communication layers, control such as timing and power control signals and data information communicated via different connections may, and typically are, different.

For those connections established by a wireless terminal, the wireless terminal and base station may choose to have a set of downlinks and/or uplinks active and the remaining links dormant. In various embodiments, the wireless terminal may choose to transmit data and/or control information flows on the link for the downlink or uplink to be active.

A wireless terminal has multiple pairs of transmitter and receiver circuits, where each transmitter/receiver pair is dedicated to a connection. Preferably, multiple transmitter/receiver pairs share the same analog device components, such as receiver/transmitter circuitry. In an exemplary embodiment, the different connections are individually synchronized and the connections are separate in the digital domain.

A make-before-break handover method implemented in accordance with the present invention comprises: the wireless terminal maintains multiple simultaneous and independent connections with the current base station and the handover candidate base station until the connection with the current base station drops. The connections with the current base station and the handover candidate base station are independently operated. During make-before-break handover, the downlink and uplink of multiple connections may remain active and all links may carry control and data flows. However, due to system and/or terminal constraints, the above-described handover behavior may be limited such that most or all downlinks of the multiple connections are active and carry both control and data streams. While multiple uplinks are active and transmit control flows simultaneously for a given device, in the exemplary embodiment only a single uplink is used to communicate the device's data flow at any given time.

Numerous additional features, advantages and details of the method and apparatus of the present invention are set forth in the detailed description which follows.

Drawings

Fig. 1 illustrates a known communication system with uplink signaling during, for example, soft handover.

Fig. 2 illustrates a known communication system with downlink signaling during, for example, soft handover.

Fig. 3 illustrates a communication system implemented in accordance with an exemplary embodiment of the present invention.

Figures 4-6 illustrate three embodiments in accordance with the present invention that maintain multiple network connections.

Fig. 7 illustrates the existence of multiple separate synchronization loops, one for each base station that may interact with a wireless terminal at any given point in time.

Fig. 8 is a block diagram illustrating in more detail an exemplary wireless terminal implemented in accordance with the present invention.

Fig. 9 illustrates a transmitter circuit that may be used as the transmitter circuit of the wireless terminal of fig. 8.

Fig. 10 illustrates a receiver circuit that may be used as the receiver circuit of the wireless terminal of fig. 8.

FIGS. 11-14 illustrate signaling and connections established as part of a make-before-break operation performed in accordance with the present invention.

Detailed Description

Fig. 3 illustrates a communication system 300 implemented in accordance with the present invention. Communication system 300 includes wireless terminal 302, base station 1304, base station 2306, and wired network 308. Communications between components of system 300 are represented by arrows and will be described below.

The wireless terminal 302 is equipped to maintain its multiple wireless connections with multiple base stations 304, 306 in parallel, i.e., multiple connections are maintained simultaneously, for example. The wireless connection connects the wireless terminal 302 with a particular base station, such as the base station 1304, and is used between the wireless terminal 302 and the base station 1304 to exchange network level and higher level data and/or control, link, and MAC layer information, i.e., data flow and/or control flow, between the wireless terminal 302 and the base station 1304. Wireless terminal 302 may establish wireless connections with more than one base station, such as base station 1304 and base station 2306, in accordance with the present invention. The technologies and/or frequency spectrums used by the different simultaneous connections may be the same or different.

In accordance with the present invention, multiple pieces of information, which may be, and typically are, different, are communicated by different simultaneous connections at any given time between the wireless terminal 302 and the base stations 304, 306. Thus, the connections that simultaneously transmit different information are independent connections, in other words, the information is transmitted on different channels.

Fig. 3 depicts two simultaneous and independent connections that are made between the wireless terminal 302 and the base stations 304, 306, the connections use the same bandwidth but different communication channels so that the connections do not interfere with each other. Arrows 310 and 312 represent communication channels.

The approach of multiple simultaneous independent connections is different from the approach of soft handover for at least the following reasons. In particular, in accordance with the present invention, signals exchanged between the wireless terminal 302 and the plurality of base stations 304, 306 convey different pieces of information, while in soft handoff, signals on the plurality of links convey the same pieces of information. Since the two channels carry different information, the mobile switching center does not have to act as a combining and/or duplicating unit. Thus, in accordance with the present invention, the base stations 304, 306 may be directly, separately and independently coupled to the wired network 308. In fig. 3, the coupling is represented by arrows 314 and 316.

A connection or channel comprises a pair of separate communication paths, a downlink and an uplink, each of which carries a separate information stream. At any given time, the downlink, uplink, or both are active for a connection. Furthermore, data and/or control signals and data and/or control flows are transmitted via the connection when the downlink or uplink is active.

According to the invention, the validity of different connections may be different and, when valid, the type of information flow transmitted via the different connections may be different. At any given time period with multiple connections to a given wireless terminal 203, wireless terminal 302 or base stations 304, 306 may choose to dynamically set a set of downlinks and/or uplinks active and, as an option, may also leave the remaining links inactive. For an active downlink or uplink, a wireless terminal or base station may choose to transmit data and/or control streams on that link. Different embodiments for connection setting will now be described.

Fig. 4-6 illustrate three embodiments of the present invention, which are performed with the base stations 1 and 2304, 306 of the communication system 300. Control flow is represented by dashed lines and data flow is represented by solid lines. The active downlink or uplink is indicated by an arrow pointing in the appropriate direction, i.e., for the downlink, the arrow points to the wireless terminal, and for the uplink, the arrow points to the base station.

In a first embodiment depicted in fig. 4, a wireless terminal 302 has connections 410, 414 with first and second base stations 304, 306, respectively. Each connection 410, 414 contains a control uplink 408, 412 and a control downlink 409, 413, respectively. Each connection 410, 414 also includes a data uplink 416, 418 and a data downlink 417, 419, respectively. Thus, in the example of fig. 4, both bi-directional control and data communications are supported for communications with the base stations 304, 306.

In a second embodiment of the invention depicted in fig. 5, a wireless terminal 302 has connections 510, 514 with first and second base stations 304, 306, respectively. Each of the first and second connections 510, 514 comprises a control uplink 508, 512 and a control downlink 509, 513, respectively. The first connection 510 also comprises a data uplink 516 and a data downlink 517. The second connection 514 contains a data downlink 519 but no data uplink. Thus, in the example of fig. 4, bi-directional control signaling is supported for the connection with the base stations 304, 306, bi-directional data communication with the base station 304 is supported, while downlink data communication is supported for the connection 514 with the second base station 306.

As shown in fig. 5, the base station 1304 has uplink (508, 516) and downlink (509, 517) connections with the wireless terminals 502 that carry control and data flows. On the other hand, base station 2306 has connections for control streams such as uplink 512 and downlink 513, but only downlink connection 519 for data streams. In the example of fig. 5, a device transmits data using a single uplink at any given time, although there are multiple active uplinks, any or all of which may be used to communicate control information.

In the third example of the invention shown in fig. 6, each wireless terminal connection 610, 614 contains an active control (609, 613) downlink and an active data (613, 619) downlink at any given time, while a single one of the wireless terminal connections 610, 614 contains both an active control uplink 608 and an active data uplink 616. In this way, at a given time, the wireless terminal may be fully engaged with the base station 304, but may only receive control and data signals from multiple base stations 304, 306.

For example, wireless terminal 602 and base station 1304 have an active control and data downlink (609, 617) and uplink (608, 616), thereby enabling bi-directional communication of the two connections to carry control and data streams. On the other hand, for base station 2306, wireless terminal 302 has active downlinks 613, 619 for control and data flows, respectively, but does not have an active uplink connection.

The wireless terminal 302 synchronizes with each other with the respective base station 304, 306 to which it is connected for the connection to be established, wherein the synchronization operation typically includes carrier frequency and timing synchronization of symbols/frames. In the case where the base stations 304, 306 are not themselves synchronized, the synchronization operations for the respective connections 310, 312 are performed independently in accordance with the present invention.

In particular, the carrier frequencies and symbol/frame timing parameters at the transmitter and receiver of wireless terminal 302 are set and/or tuned independently for each connection 310, 312. Fig. 7 illustrates the use of separate synchronization control loops 704,706 within the wireless transmitter 302 to ensure proper and independent timing synchronization of the various base stations 304,306 connected to the wireless terminal 302.

In the example of fig. 7, the wireless terminal 302 has first and second independent connections 310, 312, which may be asynchronous connections, for example. The first connection 310 is connected to a base station 1304 and the second connection 312 is connected to a base station 2306. Since the base stations 304, 306 have not been synchronized, the wireless terminal 302 maintains separate synchronization loops 704, 706 for each connection. The synchronization loop 1704 is for the first connection 1310 and the second synchronization loop 706 is for the second connection 312. Although the synchronization loops 704,706 are independently operable, they may share some common hardware, such as analog receiver circuitry, for receiving signals corresponding to the connections 310,312, while separate digital processing may be used to perform all or part of the timing control implemented in each synchronization loop 704.

Fig. 8 depicts an exemplary wireless terminal 302 of the present invention in greater detail than previous figures. The wireless terminal includes a transmitter antenna 752 coupled to a transmitter circuit 754. It also includes a receiver antenna 756 coupled to the receiver circuitry 758. The transmitter circuit 754 receives digital control and data signals to be transmitted from the bus 767. Receiver circuit 758 generates digital control and data signals from the received signal which are output over bus 767. The transmitter and receiver circuitry is responsive to timing, power control, and other signals received from other terminal components via bus 767.

As shown in fig. 8, a bus 767 couples the different components of the wireless terminal together. These components, which are coupled together, include an input device 770, an output device 772, transmitter circuitry 754, receiver circuitry 758, a processor 774 such as a CPU, and memory 760. The input device may be, for example, a numeric keypad and/or a microphone. The output devices 772 may include speakers and/or display devices. The memory 760 contains data 760 that has been received or will be sent and saved in the form of a file, such as voice, text, email, or other type of data. Before transmission, the data may be stored as packets or packetized. And the memory contains transmission routines 764, reception routines 766 and different sets of parameters 777, 779 for each connection maintained with a base station. Transmit routine 764 and receive routine 766 are executed by processor 774 and control various transmit/receive operations. The transmission routines 764 may include a synchronization loop routine and a main digital processing routine that, when executed, provide a synchronization loop and a main digital processing module (see, e.g., fig. 9), both of which may be executed at any given time for use with each base station connection that will be supported by the wireless terminal 302. Likewise, the receive routines 766 may also include a synchronization loop routine and a main digital processing routine that, when executed, provide a synchronization loop and a main digital processing module (see, e.g., fig. 10), both of which may be executed at any given time to be used for each base station connection that will be supported by the wireless terminal 302.

Transmit routines 764 and receive routines 766 are executed by processor 774 and control various transmit/receive operations. Processor circuit 774 may be configured to operate as a synchronization loop circuit for the receiver and transmitter and a main digital processing module for the receiver/transmitter, under the control of routines 766 and 774. Alternatively, dedicated hardware circuits may be used to implement such circuits and/or modules.

A transmitter and receiver system using multiple synchronization loops will now be described.

Wireless terminal 302 has multiple pairs of transmitters and receivers, each pair dedicated to a particular connection. In one embodiment of the invention, each transmitter/receiver pair is constructed with separate device components. An exemplary transmitter system 800 is described herein with respect to fig. 8, and an exemplary receiver system 900 is described with respect to fig. 9.

Fig. 9 illustrates a wireless terminal assembly 800 used to transmit signals to a base station in accordance with the present invention. The wireless terminal assembly 800 includes an analog processing module 814, a digital-to-analog converter (DAC)812, a summing unit 810, synchronization loops 806, 808, and main digital processing modules 802, 804 coupled together as shown in fig. 8. The analog processing module 814, digital-to-analog converter 812, and summing unit 810 may be part of the transmitter circuit 754 shown in fig. 8. The synchronization loops 806, 808 and digital processing modules 802, 804 may be implemented by executing routines 764 on processor 774 or using dedicated hardware circuits. The analog processing module 814 may include components such as Radio Frequency (RF) and analog filters, analog mixers, and the like. Signals transmitted to base stations 304 and 306 are processed by each of these circuits. However, such circuitry may be duplicated for transmission to the respective base stations 304, 306, thereby eliminating the need for the summing unit 810, which may require multiple modules 814 and digital-to-analog converters 812.

In an exemplary transmission operation, digital signals corresponding to the various base station connections are first generated, with each signal representing control and/or data information to be transmitted over the corresponding connection. According to the invention, the digital signals to be transmitted to the various base stations are independently processed by separate main digital processing modules 802, 804 and synchronization loops 806, 808, wherein the synchronization loops 806, 808 are used to process those signals directed to the base station to which the signals are directed. In the example of fig. 8, the main digital processing modules 802, 804 perform further digital processing, such as channel coding, on the digital signals to be transmitted over the different connections.

The base stations may not be synchronized. Thus, according to the present invention, frequency and timing corrections for synchronization are based on synchronization parameters and are performed independently by digital signal processing using digital signals for respective connections. These frequency and timing corrections are performed independently by the synchronization loops 806, 808 on a per base station connection basis.

The separate digital signals to be transmitted to the base stations 304, 306 are then added and converted into a single analog signal by the adding unit 810 and the digital-to-analog converter 812, respectively. The information on the different connections is communicated over separate communication channels, which may be, for example, OFDM communication channels implemented using, for example, different frequency tones. Thus, when combining information, the adding unit introduces the minimum interface to the information to be transmitted. The analog processing module 814 amplifies the converted analog signal and then transmits the analog signal via a wireless channel.

Fig. 10 illustrates a wireless terminal assembly 900 used to receive signals from a base station in accordance with the present invention. The wireless terminal assembly 900 includes an analog processing module 902, an analog-to-digital converter (ADC)904, a replica unit 906, demultiplexer circuits 905, 907, synchronization loops 908, 910, and main digital processing modules 912, 914, which are coupled together as shown in fig. 10. The analog processing module 902 may include components such as Radio Frequency (RF) and analog filters, analog mixers, and the like. The analog processing module 902, analog-to-digital converter 904, replica unit 906 and demultiplexer circuits 905, 907 may be implemented as part of the receiver circuit 758. And synchronization loops 908, 910 and digital processing modules 912, 914 may be implemented by executing routines 766 on processor 774 or using dedicated hardware circuits.

In an exemplary receiver operation, a received signal, such as an analog signal, is first processed by an analog device component, such as an analog filter, amplifier, or analog processing module 902. The processed signals are then converted to individual digital signals by analog-to-digital converter 904. Thereafter, the copying unit 906 copies the digital signal to form a plurality of copies of the same digital signal. Each of the multiple copies of the digital signal is further processed at the respective base station connection.

The receiver system 900 comprises separate signal splitter circuits 905, 907, synchronization loops 908, 910 and main digital processing modules 912, 914 for its connection to the base stations 310, 312, respectively, according to the invention. The frequency and timing corrections for synchronization are performed independently for each connected digital signal based on the synchronization parameters and by performing digital signal processing operations after one of the circuits 905, 907 has completed signal separation. In this example, the separation of the respective connections is performed in the digital domain.

The signal separation, timing synchronization and decoding operations are performed by the signal separation circuits 905, 907, the synchronization loops 908, 910 and the main digital processing modules 912, 914 corresponding to the respective base station connections. Thus, signals corresponding to different base stations are processed independently in the digital domain.

The main digital processing performed by the modules 912, 914 may include, for example, channel decoding operations. Because the decoding is performed by the modules 912, 914, the transmitted data and/or control signals corresponding to each individual base station are independently recovered. The recovered control and/or data information may be stored in memory 810 and/or further processed by processor 824.

According to various embodiments of the present invention, multiple transmitter/receiver pairs may share the same analog device components, such as Radio Frequency (RF) and analog filters.

There is a case in which wireless terminal 302 may maintain a connection with multiple base stations in a handover operation. In accordance with the present invention, when wireless terminal 302 performs a handoff operation, it maintains multiple simultaneous independent connections with base stations 304, 306 in neighboring areas. Exemplary handoff operations will now be discussed with respect to the communication system of fig. 3.

The wireless terminal is mobile so it encounters a new base station within its transmission range. The wireless terminal 302 establishes a new connection with the new base station 306 when it detects the presence of a new base station, such as base station 2306, and determines that the new base station 306 is a handover candidate, this operation is accomplished by communicating directly with the new base station 306, such as by providing device-specific connection establishment information to the new base station 306, and/or by communicating indirectly with the new base station, such as by having the current serving base station 304 inform the new base station 306: there is a wireless terminal 302 in the coverage of the new base station.

Preferably, during a handover operation, the new connection is established before the connection with the current base station 304 drops, thereby resulting in a make-before-break feature of the handover operation. The make-before-break feature effectively reduces or even eliminates data loss and latency that might otherwise occur in a handover.

Fig. 11-14 illustrate connections established as part of the make-before-break switching operation of the present invention. In the examples of FIGS. 11-14, both bi-directional control and data communication links are supported. The wireless terminal maintains an active uplink for each base station with which it communicates. The uplink is used to transmit control information such as power control and link layer acknowledgement to individual base stations. According to the present invention, these control information may be different for different base stations.

Fig. 11 depicts step 1 in handover. In this step, the wireless terminal 302 has a connection to a base station, such as the first base station 304. In both uplink and downlink directions, the connection communicates control information over link 1010 and data information over link 1008.

In step 2, when wireless terminal 302 approaches base station 2306, wireless terminal 302 decides to add base station 2306 as a handover candidate base station. Thus, as shown in fig. 12, the wireless terminal 302 establishes and maintains two connections, one of which is connected to the first base station 304 and the other of which is connected to the second base station 306.

According to the invention, the two connections are operated independently. For this exemplary embodiment, in the downlink, different data packets and control information are received from each of the first and second base stations 304, 306. The data packets received by different base stations 304, 306 may be different portions of the same file or message being sent, such as a voice email or text message. In the uplink, control information is transmitted to the base stations 304, 306 as indicated by the upward arrows in arrows 1010 and 1112. For example, the control information transmitted to different base stations 304, 306 may be different, as the base stations may not be synchronized. That is, in some embodiments, the transmission start times of different symbols are used by the respective base stations 304, 306 that need to perform different symbol timing synchronization with respect to signals exchanged by the different base stations 302, 304.

In the example shown in fig. 12, at any given time, a data packet is transmitted from the wireless terminal to a separate base station, such as the first base station 304. Wireless terminal 302 transmits its uplink data stream to a single base station, which is preferably the one with the best channel conditions. For example, assume that base station 1304 has the best wireless channel conditions. In this way, wireless terminal 302 transmits data packets to base station 304 via link connection 1008.

Now, assume that the radio channel state of the second base station 306 becomes better than that of the first base station 304. For transmission purposes, the wireless terminal 302 will switch to the second base station 306 and will send data packets via its connection with the second base station 306 instead of the first base station 304.

There may be an overlapping period of time at the time of switching. The benefit of having two connections during this time is very significant. For example, the wireless terminal 302 may continue to transmit its data stream to the first base station 304 to stop serving those data packets that are in transit while beginning to transmit a data stream of new and different data packets to the second base station 306. For example, the different data packets transmitted to the first and second base stations 304, 306 may comprise IP packets representing different portions of the same message or file. Since the two connections are on two different communication channels, simultaneous data transfer to the two base stations 304, 306 is possible. Alternatively, the wireless terminal 302 can first stop serving data packets that are being transmitted to the first base station 304 and then initiate a data flow of new data packets transmitted to the second base station 2306.

When the channel state of the connection of the second base station 306 improves and exceeds the channel state of the connection of the first base station 304, e.g. when the wireless terminal moves from one cell to another, the wireless terminal 302 starts to handover the data stream from the first base station 304 to the second base station 306 in a third step. This will result in the connection signal flow shown in fig. 13. In fig. 13, the uplink data flow connection between the wireless terminal and the first base station 304 has been terminated and the wireless terminal 302 has formed an uplink data flow connection 1210 with the second base station 306. Thus, in the case where data transmission to the second base station 306 is started, the data flow to the first base station 304 is stopped. In this embodiment, a single uplink is used to transmit a data stream at a given time, while all active uplink connections transmit control streams. In fig. 13, the effective uplink control flow is represented by the upward facing arrows on connections 1209 and 1211.

When the wireless terminal 302 moves out of range of the first base station 304, the respective connections 1208, 1209 are broken in step 4 of the handover of the present invention. Thus, as shown in fig. 14, the wireless terminal 302 will have a connection 1210, 1211 to the second base station 306. Thus, at the end of the handover operation, the mobile node 302 has a separate connection with a base station.

Make-before-break handover is quite different from soft handover because the multiple simultaneous connections between the wireless terminal and different base stations are independent and carry different control and/or data information. According to the invention, the connections to the current base station and the new base station are operated independently.

Specifically, in the physical layer and wireless terminal memory 760, the wireless terminal maintains separate sets 777, 779 of transmitter/receiver synchronization parameters for different connections. Further, the pieces of information for different base stations transmitted on these connections may be different in higher layers. In the downlink direction, the data and control streams from the base station to the wireless terminal may contain different pieces of information. For example, the base station may, and in various embodiments does, transmit different and independent data packets to the wireless terminal simultaneously. Similarly, in the uplink direction, the data and control streams transmitted from the wireless terminal to the base station may contain different pieces of information.

The steps of the various methods of the present invention can be implemented in various ways, such as using software, hardware, or a combination of software and hardware, to perform each of the individual steps or a combination of these steps. Various embodiments of the invention include apparatuses for performing the steps of the various methods. Each means may be implemented using software, hardware such as a circuit, or a combination of software and hardware. Accordingly, the invention is directed, inter alia, to computer-executable instructions, such as software, which control a machine or circuitry to perform one or more of the steps or signal processing operations discussed.

The timing synchronization loop of the present invention may be implemented using various techniques and/or circuits. Various Timing and Synchronization circuits and methods that may be used to implement the Timing loops used in the wireless terminals of the present invention are described in U.S. patent application 10/090,871 entitled "Method of Symbol Synchronization in Communication Systems" filed on 3, 4, 2002 and U.S. patent application 09/503,040 filed on 11, 2, 2000, both of which are hereby expressly incorporated by reference. However, alternative techniques and/or circuits may be used.

It will be appreciated that many variations of the above-described method and apparatus are possible without departing from the scope of the invention. For example, the present invention is described in terms of a wireless terminal establishing a connection with two base stations. According to the present invention, simultaneous connections between a wireless terminal and a plurality of base stations can also be established and maintained. Embodiments are also contemplated in which the wireless terminal (303) supports multiple data uplinks simultaneously with different base stations (304, 306), but only a single data downlink at any given time. For example, such a data link may be a bi-directional control link connected to the two base stations, in addition to being a control link. This embodiment is similar to the embodiment shown in fig. 5, but with the arrow 519 reversed, so that the arrow represents an uplink rather than a downlink.

It should also be understood that although the methods and apparatus of the present invention are suitable for application to Orthogonal Frequency Division Multiplexing (OFDM), they may also be used in conjunction with other communication techniques and should not be limited to OFDM systems.

Claims (16)

1. An apparatus for operating a wireless terminal to interact with a plurality of base stations including a first base station (304) and a second base station (306), comprising:

means for performing a first timing synchronization operation to synchronize the timing of the data signal with the first base station (304);

means for performing a second timing synchronization operation to synchronize the timing of the data signal with the second base station (306), wherein the first and second timing synchronization operations are performed independently and in parallel; and

means for transmitting the first data to a first base station (304); and

means for transmitting different data to the second base station (306) while transmitting the first data to the first base station (304).

2. The apparatus of claim 1, wherein the first and second electrodes are,

wherein the means for performing a first timing synchronization operation comprises means for receiving a timing control signal from a first base station (304) via a first control link (409); and

wherein the means for performing a second timing synchronization operation comprises means for receiving a timing control signal from a second base station (306) via a second control link (419).

3. The apparatus of claim 2, wherein said first and second timing synchronization operations are symbol timing synchronization operations.

4. The apparatus of claim 1, wherein said first data and said different data are different portions of a single data file.

5. The apparatus of claim 4, wherein the data file is one of an email file, an image file, and a text file.

6. The apparatus of claim 5, wherein the first and second electrodes are,

wherein the first data is stored in a first data packet and the different data is stored in a second data packet; and

wherein the transmission of the second data packet to the second base station (306) is started in the course of the transmission of the first data packet to the first base station (304).

7. The apparatus of claim 6, further comprising:

means for stopping transmission of data to the first base station (304) after ending transmission of the first data packet, while continuing transmission of data to the second base station (306).

8. An apparatus for performing a handover between base stations of a communication system, the apparatus comprising:

means for communicating with a first base station (304);

means for establishing a connection with a second base station (306);

means for transmitting different communication signals representing packets of digital data in parallel to said first and second base stations (304, 306); and

means for monitoring the quality of connections to the first and second base stations (304, 306); and

means for stopping the transfer of data to the lower quality connection.

9. An apparatus for performing a handover between base stations of a communication system, the apparatus comprising:

means for communicating with a first base station (304);

means for establishing a connection with a second base station (306);

means for transmitting different communication signals representing packets of digital data in parallel to said first and second base stations (304, 306); and

means for monitoring the quality of connections to the first and second base stations (304, 306); and

means for changing the base station (304, 306) to which the data is being transmitted when the quality of the connection being used to transmit the data is worse than the quality of the data connection of the base station not transmitting the data.

10. The apparatus of claim 8 or 9, wherein,

wherein the different communication signal is a data signal representing a packet of digital data; and

wherein said means for transmitting different communication signals representing packets of digital data in parallel to said first and second base stations (304, 306) comprises means for transmitting a first packet of data to said first base station (304) and a second packet of data to said second base station (306), each of the first and second packets of data comprising different data derived from the set of data to be transmitted.

11. The apparatus of claim 10, wherein the set of data to be transmitted is one of an email message, a voice message, and a text message.

12. The apparatus of claim 10, further comprising: means for transmitting start times using different symbols when transmitting symbols representing at least part of said first and second data packets to said first (304) and second (306) base stations.

13. An apparatus for implementing a communication system, the apparatus comprising:

means for providing a plurality of base stations (304, 306) for interacting with a mobile communication device (302);

means for operating at least first and second base stations (304, 306) of said plurality of base stations to receive in parallel from said mobile communication device (302) different data to be transmitted via a wired asynchronous communication network (308); and

operating the first and second base stations (304, 306) to provide the received data to devices of the wired asynchronous communication network (308).

14. The apparatus of claim 13, wherein said different data is included in a first data packet transmitted by said first base station (304) and a second data packet transmitted by said second base station (306).

15. The apparatus of claim 14, wherein said first and second data packets correspond to different portions of at least one of an email message, a voice message, and a text message sent by said mobile communication device.

16. The apparatus of claim 15, further comprising:

means for operating the first and second base stations to perform independent asynchronous symbol timing synchronization operations in conjunction with the mobile communication device.