Patent Application
20080107095
The present invention relates generally to wireless communications, and more particularly to a communication system operating in a licensed RF band and an unlicensed RF band.
Wireless communication devices generally operate in either licensed radio frequency (RF) bands or unlicensed RF bands. Radiotelephone service providers generally acquire licenses to operate a wireless communication system in one or more of a plurality of licensed RF bands. These systems employ multiple methods to allow multiple access by multiple mobile stations on a common band of frequency channels. These systems generally operate in licensed RF bands. Other systems operate in unlicensed RF bands. Systems that operate in licensed RF bands have control over the frequencies and channels and how they are operated on. This allows the operator to ensure reliability of data, and in particular, control information used to control traffic communicated with devices in communication therewith. Systems operating in unlicensed RF band do not have this control and data transmission error occur as a result of uncoordinated transmissions.
One access technique, frequency division multiple access (FDMA), allows multiple access by assigning the mobile stations to different frequency channels within the RF band. Some of these systems employ frequency hopping, wherein data is transmitted to and from the intended mobile station while periodically changing the frequency channel. The periodic channel frequency hopping occurs on a regular time interval known as a frame. Coordinated frequency hopping systems use predetermined hopping patterns, or hop-sets, wherein the hop-sets are coordinated between all mobile stations to ensure that the signals to and from two or more mobile stations do not occur simultaneously on the same frequency channel. Uncoordinated frequency hopping does not coordinate the hop-set between mobile stations resulting in the periodic occurrence of simultaneous signal transmission on the same frequency. Such simultaneous transmissions are referred to as channel collisions. Data reception errors occurring during a channel collision are referred to as data collisions. Uncoordinated frequency hopping within this type of system is generally not used as the channel collisions and resultant data collisions will occur. The FCC has prohibited coordinated frequency hopping within the Industrial Scientific and Medical (ISM) bands in order to avoid spectrum aggregation by a single type of service.
Systems such as Bluetooth and 802.11 wireless communication systems, for example operate within the ISM bands. To avoid data collisions these systems may monitor the band and choose to operate only in unoccupied sub-bands. These systems may also change sub-bands as the result of the detection of interferer signal strength or the detection of signaling errors indicative of a channel collision with another transmitting station. However channel collisions still occur as devices must sense the interference caused by a channel collision in order to change the frequency sub-band.
Therefore, what is needed is a method for a communication system to operate in a licensed RF band and an unlicensed RF band.
The various aspects, features and advantages of the present invention will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description of the Drawings with the accompanying drawings described below.
A method for a communication system to operating in a licensed radio frequency (RF) band and an unlicensed RF band is disclosed. The method comprises communicating with mobile stations in both a licensed RF band and an unlicensed RF band. The base station communicates control information to the mobile station in the licensed RF spectrum. Traffic channels established between the base station and the mobiles reside in the unlicensed spectrum. The method also comprises determining that a first data set, which is to be sent to a first device, and a second data set, which is to be sent to a second device, are scheduled to be transmitted in the unlicensed RF band simultaneously on a first frequency, i.e. a channel collision. The data collision is avoided between the two data sets, by transmitting the first data set on the first frequency hopping frequency, while the second data set is delayed, also known as muted. The first data set is thereby transmitted unambiguously and data collisions are avoided in the first device. The final step is transmitting the second data set on a second frequency hopping frequency, sequentially next in the frequency hop pattern at the next frame.
The second data set is thereby transmitted unambiguously with a delay of at least one frame. Thus the hopping channels are uncoordinated, since the original uncoordinated hopping sequences are unmodified except for the muting of the transmission to the second device during the channel collision. Data collisions are avoided in the second device during the transmission of the first data set by a determination that the second device is not the intended recipient, and suspension of data reception until another frame.
The base station communicates control information with the mobile station in the licensed RF spectrum in one exemplary embodiment. In another exemplary embodiment, the base station communicates using code division multiple access or wideband code division multiple access techniques in the licensed RF band and uncoordinated frequency hopping patterns in the unlicensed RF band.
Due to RF spectrum limitations, an increase in users and the cost of RF spectrum licenses, wireless telecommunications service providers could benefit from using unlicensed RF spectrum to compliment the licensed spectrum portion of their systems. Although the spectrum is unlicensed, use-requirements still apply. FCC requirements for transmission in the industrial, scientific and medical (ISM) bands, for instance, requires that transmissions use uncoordinated frequency hopping with power limitations.
One example is the use of unlicensed RF bands to augment GSM radiotelephone services. The GSM system uses non-hopping channel frequencies with high transmission power for broadcast control channels, which are unsuitable for transmission in the ISM bands. For other control channels and traffic channels the GSM system uses coordinated frequency hopping in which each mobile station uses the same set of channel frequencies and hopping pattern, and a unique time offset of the hopping pattern determined by the mobile allocation index offset (MAIO). In this way the system can accommodate one communication signal for each hopping channel without the occurrence of channel collisions.
The base station 104 receives messages from the BCS 102 and transmits the messages to the intended wireless devices under an uncoordinated frequency hopping scheme. Communications between the base station 104 and the first wireless device 105 share a first uncoordinated hop-set while the base station 104 and the second wireless device 107 share a second uncoordinated hop-set while. There is no coordination between the first uncoordinated hop-set and the second uncoordinated hop-set, however these hop-sets may comprise common frequency channels such that frequency channel collisions may occur. The wireless devices may be mobile stations or other user equipment that communicate with a serving node, such as the exemplary base station 104 of the communication system 100 in
Turning to
The mobile station also includes a message scheduling module, that schedules traffic information to be sent in the unlicensed RF band and that schedules control information which is associated with the traffic information to sent in the licensed RF band.
The wireless communication device 200 of the present invention can be adapted to communicate in a frequency hopping wireless communication may also comprise a channel collision detection module 224 that detects when received messages are not intended to be received by the mobile station and a transmission scheduling module 225 both coupled to the microprocessor 204.
A base station 104 of the wireless communication system may include a transmitter 120 and a receiver 122 for communicating with a plurality of wireless communication devices. The base station 104 would also include a message reception module 124, that receives messages from the core network which are to be transmitted to one of a plurality of wireless communication devices. The base station may also include a frequency hop pattern generation module 126. The frequency hop pattern generation module 126 determines the frequency hop-set pattern for each device of the plurality of devices. The frequency hop-set patterns are uncoordinated from device to device. The base station 104 also includes a channel collision detection module 128 that detects when received messages are scheduled to be transmitted on the same frequency at the same time and a message scheduling module that reschedules or delays transmission of a data set that was determined to collide with another data set.
The base station 104 communicates control information with the wireless device on control channels which are transmitted within the licensed RF spectrum. In one exemplary embodiment, the base station 104 is a GSM communication system. The base station 104 will identify that the wireless device 105 can communicate in both the licensed and unlicensed RF spectrum, also known as RF band. The network will then assign at least one traffic channel in the unlicensed RF spectrum using the control channels in the licensed RF band.
In the exemplary embodiment, GSM multi-frame types I-IV contain the control channels used for general link maintenance. These control channels are not mapped to a channel in the unlicensed radio frequency band. The GSM multi-frame types V and VI, contain traffic channels (TCH's) and at least two control channel that are associated with the traffic channels, the slow associated control channel (SACCH) and the fast associated control channel (FACCH). The TCH portions are candidates for transmission in the unlicensed RF band. However, the SACCH and the FACCH are mapped to at least one channel in the licensed RF band. The licensed RF band will provide greater reliability for these control channels. The unlicensed RF band is susceptible to greater interference as there is less or no regulation. The TCH therefore can be assigned to a channel in the unlicensed RF band while the control channels associated with the particular control channel are assigned to a channel in the licensed RF band to maintain reliable control over the respectively associated TCH.
In one exemplary embodiment, shown in
In one exemplary embodiment, shown in
In this exemplary embodiment, SDCCH is used to more reliably send and receive on a licensed channel frequency the data normally sent with the TCH on the SACCH and FACCH. The SDCCH is sometimes referred to as a as ⅛ rate traffic or TCH/8. Each half rate traffic channel, i.e. TCH/2, which is moved to a channel in the unlicensed RF band requires one new TCH/8 to be added on the licensed RF band.
In another exemplary embodiment, shown in
In this embodiment, the TCH 508 is mapped to the unlicensed RF band and the SACCH 504 is mapped on the channel in the licensed RF band 502. In lieu of the FACCH it provides a new SACCH/DFACCH multi-frame type, mapped onto a licensed channel frequency. In this exemplary embodiment, the new SACCH/DFACCH supports 18 unlicensed traffic channels with SACCH messaging at the usual rate (480 ms/4 block message), and one on-demand FACCH (DFACCH) shared by the 18 users on an as-needed basis. One bit is used on uplink SACCH (all blocks) for FACCH request, and one bit is used in the down link SACCH for a grant of the FACCH. If the Network needs to perform a handover, it sets the bit in the SACCH of the specific mobile station, and then transmits starting in the next FACCH. When the mobile station needs to use the FACCH to contact the BS, it requests the FACCH by setting the request bit and then monitoring the grant bit. Whenever the grant bit is set in the SACCH the mobile station starts to monitor the DFACCH.
In the above exemplary embodiments, the channel conditions are communicated from the mobile station by transmitting traffic channel conditions of at least one traffic channel in the unlicensed RF band over an uplink control channel in the licensed RF band. Control channel conditions are communicated by transmitting control channel conditions of at least one control channel in the licensed RF band over a control channel in the licensed RF band. Other control channel conditions may be transmitted in the licensed RF band over a control channel which is also in the licensed RF band. The mobile station will receive control information over a downlink control channel in the licensed RF band, wherein the control information is related to the traffic information in the unlicensed RF band.
The control information that may be communicated or exchanged over the licensed RF band is handoff information, an end call message, a neighbor list, a neighbor report, a power control message, a timing control message or the like. In one exemplary embodiment, portions of the dedicated channel are used for traffic information when control information is not being sent.
It is understood by one skilled in the art that the present invention may apply to communications systems that operate under the GSM standard but also under EDGE, CDMA, WCDMA, TDMA UMTS, and any communication system that operates in both a licensed and an unlicensed RF band. For example traffic channel in the system be a CDMA channel. The control channel may also be a CDMA channel. The CDMA traffic channel may be in the unlicensed RF band while the CDMA control channels are in the licensed RF band. In another exemplary embodiment, the unlicensed band requires a frequency hopping pattern to be used for channelization, such as is required by the FCC for operation in the ISM band for example.
In yet another exemplary embodiment, the traffic channel (TCH) is a plurality of frequencies of a frequency hopping pattern. In this exemplary embodiment, the frequency hopping pattern is uncoordinated and in the unlicensed RF band.
Although two data sets are used for exemplary purposes throughout this disclosure, it is envisioned that a plurality of data sets may be scheduled to be transmitted simultaneously and on the same frequency as the individual frequency hop-sets associated with each device are uncoordinated between the devices. As the number of wireless devices communicating in the communication system increases, the potential for data collisions also increases. Therefore the base station 104 must check the scheduling of all messages, in accordance with the above method, to be transmitted to avoid collisions.
Referring now to the exemplary flowchart in
Continuing with reference to
The base station 104 should determine which data set should be transmitted after determining 604 that a channel collision will occur. In one exemplary embodiment, the base station 104 or the base station controller 102, will send the data set received first in time at the base station 104 or the base station controller 102. In this exemplary embodiment, the data sets are processed on a first in first out (FIFO) basis. In another exemplary embodiment, the data set to be sent first is randomly selected. If multiple data sets are scheduled to collide, all except one data set would have to be rescheduled. It should be noted that multiple transmissions can occur at the same time, however multiple transmission can not occur at the same time on the same frequency without causing data collisions and resultant data errors in the wireless device receivers. In yet another embodiment, priority is given according to the needs of the wireless device, whereby voice data may be given higher priority than other types of data, for example. It is understood by one skilled in the art that there are a plurality of methods for determining which data set to send and in what order, and the disclosure is not limited to those exemplary embodiments listed herein.
Moving to
For example, in an exemplary GSM system, a GSM traffic channel (TCH) might be modified to include a temporary mobile station identity code (TMSIC), which is the unique sub-channel code having a unique value for every wireless device receiving a data set, i.e. data transmissions, from the base station on a particular hop-set of hopping frequencies channels. Upon decoding the TMSIC the second mobile station will determine that the received TMSIC is different that it's TMSIC assignment and discard the received data or suspend reception.
Referring to
In the above exemplary embodiments, the methods allow for the avoidance of data collisions in the downlink transmissions on the traffic channels from base station to mobile station, i.e. wireless device. Analogous techniques may be applied for avoiding data collisions on the uplink transmissions, i.e. transmissions between mobile stations and the base station. This applies to the situation in which the uplink and down-link hop sets are uncoordinated. However it is anticipated that coordination of up-link and down-link hop-sets will be allowed. In the cases such where the downlink and uplink channels are assigned in pairs, one exemplary embodiment provides a method where the uplink channel assignment follows the downlink assignment on the same frequency channels. In another exemplary embodiment, such as in the GSM case, the uplink channel follows the downlink channel with a fixed frequency offset. According to this approach, whenever a downlink channel collision occurs there will necessarily be a corresponding uplink collision. Thus, in this exemplary embodiment, when a wireless device receives a downlink data set during a channel collision as in accordance with one of the approaches described above, it will then transmit its uplink data set on the scheduled uplink transmission period, whereas if a wireless device does not receive a data set during a channel collision it will refrain from transmitting its data set on the scheduled uplink period, and wait until the next scheduled uplink period to transmit the data set on the next channel frequency in the hop-set, thereby avoiding an uplink data collision.
While the present inventions and what is considered presently to be the best modes thereof have been described in a manner that establishes possession thereof by the inventors and that enables those of ordinary skill in the art to make and use the inventions, it will be understood and appreciated that there are many equivalents to the exemplary embodiments disclosed herein and that myriad modifications and variations may be made thereto without departing from the scope and spirit of the inventions, which are to be limited not by the exemplary embodiments but by the appended claims.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10750277 | Dec 2003 | US |
| Child | 11972109 | Jan 2008 | US |
