Expanding cell radius in a wireless communication system

The present invention provides a method and an apparatus for a wireless communication between a base station and at least one mobile station. The method includes receiving a request for a data rate from the mobile station on a reverse link channel to the base station. The method further includes, in response to the request, skipping a first slot after a delay for a portion of a slot on a forward link transmission before transmitting a data packet in a second slot. By beginning the forward link transmission at the start of the second slot, for example, a software module may cause the base station to skip a slot immediately after the half slot delay. This additional delay of one slot or a portion of the slot may expand radius of a cell for a wireless communication between the base station and the mobile station in a relatively high-speed wireless data network.

FIELD OF THE INVENTION

This invention relates generally to telecommunications, and more particularly, to wireless communications.

DESCRIPTION OF THE RELATED ART

Wireless communications systems or mobile telecommunication systems typically provide different types of services to different users or subscribers of wireless communication devices. The wireless communication devices may be mobile or fixed units and situated within a geographic region across one or more wireless networks. The users or subscribers of wireless units or communication devices, such as mobile stations (MSs) or access terminals or user equipment may constantly move within (and outside) particular wireless networks. A wireless unit may encompass additional features and applications than typically available on a conventional cellular phone. Examples of different features and applications include e-mail service, Internet access, audio-video interfaces for music and media content streaming.

A wireless communications system generally includes one or more base stations (BSs) that can establish wireless communications links with wireless units. Each wireless unit has an active set, which comprises a set of base stations with which it may communicate. Base stations may also be referred to as node-Bs or access networks. To form the wireless communications link between a wireless unit and a base station, the wireless unit accesses a list of available channels (or carriers) broadcast by the base station. To this end, a wireless communications system, such as a spread spectrum wireless communications system, may allow multiple users to transmit simultaneously within the same wideband radio channel, enabling a frequency re-use based on a spread spectrum technique.

In a high speed wireless data network, a mobile station provides feedback and data rate requests on a reverse link channel to efficiently utilize the forward link transmission bandwidth. In an Evolved Data Optimized (EVDO) system, for example, the mobile station sends a request for a data rate in every 1.67 ms slot via the Data Request Channel (DRC). To synchronize and simplify decoding, the EVDO air interface standard requires that if a base station sends any data packet to the mobile station, the base station must send that data packet using the exact same data rate as that requested by the mobile station over the DRC. Additionally, the base station must send the data packet in the next slot after the DRC has been decoded.

However, such a timing restriction imposes a hard limit on the radius of a cell because all the delays within a wireless communication system must meet the requirement that the base station must send the packet to the mobile in the next slot. The cell radius refers to an allowed delay over an air interface, i.e., the total delay budget without the delay from a receive antenna to a transmit antenna at a base station. The total delay budget includes the time it takes to decode the DRC, send a DRC value from a reverse link modem to a forward link modem, schedule a user among all the active users in a sector, encode a forward link packet for the selected user except a transmission delay within the base station from a radio to an antenna connector.

In addition, the EVDO standard further restricts that the base station decode the DRC only at the end of the DRC length slot. For example, if the DRC length=2, the DRC decoder determines the DRC value after 2 slots. Although this requirement allows the mobile station to use relatively lower power when using larger DRC length, so that the base station gets the combining gain, this requirement forces the base station to only have less than half a slot turn around time to start transmitting if the base station has selected a particular user, regardless of the DRC length.

Referring toFIG. 3, a conventional forward link transmission immediately starts after a half slot at the end of a data rate channel (DRC) length on the reverse link transmission. For example, a DRC length of 4 is shown, for which a decoder may determine a DRC value after 4 slots. In other words, the EVDO standard imposes a restriction over a base station to decode the DRC only at the end of the DRC length slot(s), limiting the radius of a cell. Accordingly, a larger cell having an expanded radius may not be supported by the forward link transmission and the reverse link DRC transmission consistent with the EVDO standard requirements. For example, due to the above set forth restrictions, the cell radius is limited and is unable to support a boomer cell (larger than 32 miles) configuration.

One approach may increase the cell radius, i.e., in a situation when it takes longer to receive the mobile station's DRC, (with a bigger cell radius, air interface propagation time is longer) the base station is still able to send out the data packet to a user in the next DRC slot. However, the base station performs an early decoding of the DRC, i.e., without waiting until the end of DRC length. To do such an early decoding successfully, the DRC power is increased, which in turn increases reverse link interference. Since the forward link capacity of the EVDO system result in a significantly high reverse link capacity sacrifice, any further increase in the reverse link interference may result in more reduction in the overall system capacity.

SUMMARY OF THE INVENTION

In one illustrative embodiment of the present invention, a method is provided for a wireless communication between a base station and at least one mobile station. The method includes receiving a request for a data rate from the at least one mobile station on a reverse link channel to the base station. The method further includes, in response to the request, skipping a first slot after a delay for a portion of a slot on a forward link transmission before transmitting a data packet in a second slot.

In another illustrative embodiment of the present invention, an article comprising a computer readable storage medium storing instructions that, when executed cause a base station to receive a request for a data rate from the at least one mobile station on a reverse link channel to the base station and skip a first slot after a delay for a portion of a slot on a forward link transmission in response to the request before transmitting a data packet in a second slot.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions may be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time-consuming, but may nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

Generally, a method and an apparatus are provided for expanding radius of a cell for a wireless communication between a base station (BS) and at least one mobile station (MS) associated with a high-speed wireless data network. The base station may obtain data rates for a forward link transmission based on the feedback on a reverse link from the mobile station. In a wireless communication system, the base station may start transmission to the mobile station after a desired delay, i.e., in a subsequent period instead of an available delay for only half a slot, such as a time slot of a fixed duration based on a particular standard. The base station may comprise a software module that delays the scheduling of a request for a data rate. In response to the request, the software module may skip a first slot after a half slot delay on the forward link transmission before transmitting a data packet in a second slot. That is, the base station may schedule the forward link transmission of a user to start to the mobile station in the second slot. By beginning the forward link transmission at the start of the second slot, the software module may cause the base station to skip a slot immediately after the half slot delay. This additional delay of one slot or a portion of the slot may expand radius of a cell for a wireless communication between the base station and the mobile station.

Referring toFIG. 1, a wireless communication system100is illustrated to include a base station (BS)110that may start transmission to at least one mobile station (MS)115after an additional delay, i.e., in a subsequent period instead of a typical delay of only a half slot according to one illustrative embodiment of the present invention. The additional delay may expand radius of a cell for a wireless communication between the base station110and the mobile station115.

The base station110may be associated with a high-speed wireless data network to provide the wireless connectivity to the mobile station115according to any desirable protocol. Examples of such a protocol include a Code Division Multiple Access (CDMA, cdma2000) protocol, an Evolved Data Optimized (EVDO, 1XEVDO) protocol, a Universal Mobile Telecommunication System (UMTS) protocol, a Global System for Mobile communications (GSM) protocol, and the like.

Examples of the mobile station115may include a host of wireless communication devices including, but not limited to, cellular telephones, personal digital assistants (PDAs), and global positioning systems (GPS) that employ the wireless communication system100to operate in a high-speed wireless data network. Other examples of the mobile station115may include smart phones, text messaging devices, and the like.

Consistent with one embodiment, the mobile station115may transmit messages to the base station110over a reverse link120. In the wireless communication system100, a wireless communication between the base station110and the mobile station115may occur over an air interface135via a radio frequency (RF) medium that may use a code division multiple access (CDMA) protocol to support multiple users. A forward link140may provide messages to the mobile station115. The messages may include traffic packets and signaling messages.

The base station110may receive data rate requests, such as a request148over the reverse link120a reverse link channel, such as in a data request channel (DRC)150for the purposes of starting transmission on the forward link140. The mobile station115may send the request148for a data rate to efficiently utilize the bandwidth available on the forward link140. The request148may indicate an estimate for the data rate that the mobile station115may be able to receive data from the base station110over the forward link140. For example, the mobile station115may indicate a data rate of 2.4 megabits per second, 1.8 megabits per second, and the like.

In response to the request148, the base station110may begin a forward link transmission155after a delay of at least one slot longer than a typical half slot delay. That is, the base station110may initiate transmission on the forward link140during a next period of a number of slots associated with the data request channel (DRC)150length. Examples of the number of slots associated with the DRC length include 1, 2, 4, or 8 configurable slots in the wireless communication system100depending upon a desirable application.

For example, in an EVDO compliant wireless communication system, the mobile station115may send the request148in a slot of duration, such as 1.67 milliseconds. The mobile station115may send the request148to indicate a data rate that the base station110may use for the forward link transmission155to send a user data packet to the mobile station115. The forward link transmission155may include traffic packets and signaling messages based on the CDMA2000 1xEV-DO specification, which uses a frequency band with channel bandwidth (1.23 MHz) and chip rate (1.2288 Mcps). In CDMA2000 1xEV-DO, for example, each forward link frame is 26.666 msec and consists of 16 slots. Like the forward link frame, the reverse link frame is 26.666 msec and consists of 16 slots.

By using the data rate indicated by the request148for the forward transmission link155, the base station110may communicate with the mobile station115. To this end, the base station110may comprise a receive (RX) antenna160aand a transmit (TX) antenna160b. The base station110may further comprise to an antenna connector165to couple the receive antenna160aand the transmit antenna160bto a radio170. The radio170, in one embodiment, may include a reverse link (RL) modem175(1) and a forward link (FL) modem175(2).

The FL modem175(2) may allocate one or more transmission or signaling resources for the forward link transmission155. Examples of the signaling or transmission resources include a number of time slots or a number of frequency sub-bands or a number of spatial dimensions allocated to a particular transmission mode. To this end, the FL modem175(2) may use the time slots for the forward link transmission155to the mobile station115. The RL modem175(1) may process the transmissions on the reverse link120. In particular, the RL modem175(1) may process the time slots on the reverse link120.

To schedule the forward link transmission155, the base station110may further comprise a software (SW) module180that may determine a cell size, i.e., the radius of a cell. In one embodiment, the cell size refers to an air time delay available to the base station110to transmit data to the mobile station115at a desired data rate indicated by the mobile station115in a previous period of a DRC length. The software module180may enable an additional delay of at least one slot beyond a typical half slot delay available to the base station110, increasing range of a cell size or expanding the cell radius.

In particular, the base station110may communicate with the mobile station115within a cell185. However, by gaining another slot of delay, the base station110may skip a slot immediately after the half slot on the forward link transmission155. In this way, the cell size185may increase to a larger cell190, expanding a cell radius195. As used herein, the term “the cell radius 195” refers to increase in availability of one or more radio resources, such as radio frequency (RF) resources, that may be used to form a cell as well as the various features that may be provided to the mobile station115by the base station110. For example, the software module180may enable the mobile station115to transmit at a relatively longer distance.

In other words, the software module180enables transmission with a larger delay available to increase or provide an extended range for the larger cell190. That is, in one embodiment of the present invention, the software module180may provide an additional delay of at least one slot over a typically available delay of a half slot so that the base station110may schedule the forward link transmission155to the mobile station115to start transmission on a next slot. By providing this additional delay of at least one slot, the cell185may expand in radius to the larger cell190since an additional one slot becomes available for one or more functions including decoding of a wireless communication.

Consistent with one embodiment of the present invention, the software module180may control the reverse link modem175(1) and the forward link modem175(2) to skip a slot immediately after a half slot delay in the forward link transmission155. By skipping a slot after the half slot delay, the radio170at the base station110may increase the interface delay over the air interface135since the forward link transmission155and the DRC transmission150on the reverse link120may be now one and a half slot apart.

Referring toFIG. 2, various delays associated with the wireless communication in the wireless communication system100between the base station110and the mobile station115have been illustrated according to one embodiment. For example, in a high-speed wireless data network such various delays may include an interface delay200which defines an expansion range for the cell radius195in accordance with one embodiment of the present invention.

In one embodiment, the reverse link modem175(1) at the base station110may comprise an amplifier (AMP)205(1) coupled to a decoder210. The decoder210may decode the request148from the data request channel150on the reverse link120. The amplifier205(1) may amplify a signal received over the receive antenna160a. Likewise, the forward link modem175(2) may comprise an amplifier205(2) coupled to a modulator215, in turn, coupled to a scheduler and/or encoder220. The scheduler and/or encoder220may encode the user data packet to be transmitted to the mobile station115from the base station110before for the modulator215modulates the user data packet. The amplifier205(2) may amplify the modulated data packet for transmission via the transmit antenna160bover the forward link140.

In operation, the base station110may consume time to decode the request148in the data request channel150using the decoder210. However, a delay may occur on the reverse link120in sending a DRC value from the reverse link modem175(1) to the forward link modem175(2). In other words, a reverse link (RL) delay225and a forward link (FL) delay230may occur for the request148to be met. In addition, a network delay235occurs from the receive antenna160aand the transmit antenna160b. While the reverse link delay225and the forward link delay230indicate the air interface delay200, the network delay235includes a delay associated with scheduling a user among the active users in a sector, encoding the user data packet on the forward link transmission155for the selected user, a transmission delay present within the base station110from the radio170to the antenna connector165. The air interface delay200indicates the cell radius195based on a total delay budget240without the network delay235.

However, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that the present invention is not limited to expansion of the cell radius195. In alternative embodiments, the software module180may enable the base station110to provide different capabilities and/or additional capabilities to enhance the range of the wireless communication between the base station110and the mobile station115.

According to one embodiment, the mobile station115may transmit messages or signals to one or more active base stations using one or more associated reverse links. Pseudo noise offsets (PN offsets) associated with each of the active base stations are included in an active set list, which is typically stored by a radio network controller typically coupled to the base station110. The mobile station115may receive messages and/or signals over the forward link140from one of the active base stations, which is generally referred to as the serving base station or the serving sector. The 3rd Generation Partnership Project (3GPP) standard defines the role of a serving radio network controller based on 3GPP specifications.

Besides the messages or signals, the mobile station115may receive traffic packets, such as data packets. Often the traffic packets include information that is intended for the user of the mobile station115. For example, traffic packets may include voice information, images, video, data requested from an Internet site, and the like. In contrast, signaling messages are used to provide information intended to be used by the mobile station115and/or other elements of the wireless communication system100. Specifically, signaling messages may include configuration messages, setup instructions, switch instructions, handoff instructions, and the like.

Referring toFIG. 4, the forward link transmission155and a reverse link transmission of the data rate control150channel is shown in accordance with one illustrative embodiment of the present invention the forward link transmission155may start after a delay of an additional slot, such as a first slot400. In other words, the base station110may skip the first slot400before starting the forward link transmission155after a half slot300delay. The half slot300delay after a DRC length of 2 is indicated in the DRC channel150transmission. By skipping the first slot400, the base station110may start transmission to the mobile station115on the forward link120at the beginning of a second slot405. In this way, the base station110may increase the cell radius195of an existing cell, such as the cell185to the larger cell190.

In other words, even though the EVDO standard restricts that the base station110may decode the DRC150only at the end of the DRC length305slot(s), limiting the cell radius195of the cell185the larger cell190having the cell radius195may be supported by the forward link transmission155and the transmission of the DRC channel150on the reverse link120, as shown inFIG. 3consistent with the EVDO standard requirements.

Turning now toFIG. 5, scheduling of the forward link transmission155of a user to the mobile station115is illustrated in a particular slot consistent with one exemplary embodiment of the present invention. The base station110may receive the request148for a data rate from the mobile station115on a reverse link channel, such as the data request channel (DRC)150in transmission over the reverse link (RL)120, as indicated in block500.

The software module180may determine whether the number of slots in a request period, i.e., the DRC length is >1 at a decision block505. To this end, the decoder210at the base station110may determine whether the DRC length305is such that the decoder210can determine a DRC value after one or more slots. If so, the decoder210may indicate to the software module180that the first slot140may be skipped. In this way, at block510, the software module180may skip the first slot140after the half slot300delay on the forward link transmission155before transmitting a data packet in the second slot405, as shown inFIG. 4.

However, the first slot140may be used for preparing to decode a reverse link transmission during the second slot405, as shown in block515. The scheduler and/or encoder220at the base station110may schedule the forward link transmission155of a user to start to the mobile station115in the second slot405. By beginning the forward link transmission155at the start of the second slot405, the software module180may cause the base station110to skip a slot immediately after the half slot300delay as shown in block520.

When at the decision block505the software module180determines that the number of slots in the request period is >1, the base station110may delay the scheduling of the forward link transmission155by the scheduler220and/or encoder220, as shown in block525. Another decision block530may indicate whether the request148is a request for a new data rate. If the request148is for a new data rate, the method transitions to the block515.

Alternatively, if the request148is indicated to be a request, which has been previously received for a data rate at the base station110from the mobile station115, a decision block535determines whether a second time request is same as the preceding a first time request for a data rate. If the two consecutive requests are the same, the software module180may cause the scheduler220at the base station110to schedule the forward link transmission155to start at the beginning of the second slot405. Conversely, if the consecutive second request is not the same as the earlier request for a data rate at the decision block535, the software module180may delay the scheduling, as indicated in block525.

Referring toFIG. 6, scheduling the request148for a data rate on a reverse link channel from the mobile station115to the base station110shown inFIG. 1is illustrated in accordance with one embodiment of the present invention. The software module180may receive a value, such as a new value for each slot associated with the request148on the data request channel (DRC)150, at block600. The software module180may compare the new value with another value, such as an old value received previously for a data rate by the base station110from the mobile station115, as indicated in block605.

A decision block610may ascertain whether the old value and the new value of the data rate are different. If the two values are indicated to not be the same at the decision block610, the software module180may mark another value as an old value associated with the first slot400, as shown in block615. At block620, the software module180may cause the scheduler220to schedule the request148.

However, if at the decision block610, the software module180determines that the new value is different than the old value, which has been received previously, the software module180may replace the old value with a new value associated with the first slot400, at block625. After replacing the values, the software module180may delay the scheduling of the request148, as block630. In this way, the base station110may obtain data rates for the forward link transmission155based on the feedback on the reverse link140from the mobile station115.

In one embodiment, a high-speed wireless data network may wirelessly communicate mobile data at a speed and coverage desired by individual users or enterprises. According to one embodiment, the high-speed wireless data network may comprise one or more data networks, such as Internet Protocol (IP) network comprising the Internet and a public telephone system (PSTN). The 3rd generation (3G) mobile communication system, namely Universal Mobile Telecommunication System (UMTS) supports multimedia services according to 3rd Generation Partnership Project (3GPP) specifications. The UMTS also referred as Wideband Code Division Multiple Access (WCDMA) includes Core Networks (CN) that are packet switched networks, e.g., IP-based networks. Because of the merging of Internet and mobile applications, the UMTS users can access both telecommunications and Internet resources. To provide an end-to-end service to users, a UMTS network may deploy a UMTS bearer service layered architecture specified by Third Generation Project Partnership (3GPP) standard. The provision of the end-to-end service is conveyed over several networks and realized by the interaction of the protocol layers.

While the invention has been illustrated herein as being useful in a telecommunications network environment, it also has application in other connected environments. For example, two or more of the devices described above may be coupled together via device-to-device connections, such as by hard cabling, radio frequency signals (e.g., 802.11(a), 802.11(b), 802.11(g), Bluetooth, or the like), infrared coupling, telephone lines and modems, or the like. The present invention may have application in any environment where two or more users are interconnected and capable of communicating with one another.

Those skilled in the art will appreciate that the various system layers, routines, or modules illustrated in the various embodiments herein may be executable control units. The control units may include a microprocessor, a microcontroller, a digital signal processor, a processor card (including one or more microprocessors or controllers), or other control or computing devices as well as executable instructions contained within one or more storage devices. The storage devices may include one or more machine-readable storage media for storing data and instructions. The storage media may include different forms of memory including semiconductor memory devices such as dynamic or static random access memories (DRAMs or SRAMs), erasable and programmable read-only memories (EPROMs), electrically erasable and programmable read-only memories (EEPROMs) and flash memories; magnetic disks such as fixed, floppy, removable disks; other magnetic media including tape; and optical media such as compact disks (CDs) or digital video disks (DVDs). Instructions that make up the various software layers, routines, or modules in the various systems may be stored in respective storage devices. The instructions, when executed by a respective control unit, causes the corresponding system to perform programmed acts.