Central controller and methods for interference mitigation in TDMA networks using randomly allocated service periods

Embodiments of a central controller and methods for interference mitigation in TDMA networks are generally described herein. In some embodiments, the central controller mitigates co-channel interference by randomizing locations of channel time allocations within superframes.

TECHNICAL FIELD

Embodiments pertain to wireless networks that employ time-division multiple access (TDMA). Some embodiments pertain to wireless networks, such as Wireless Personal Area Networks (WPANs), which may use a central controller to coordinate communications between pairs of communication stations. Some embodiments pertain to wireless networks used to communicate audio-visual (A/V) including compressed video.

BACKGROUND

One issue with wireless networks that operate in an unlicensed portion of the frequency spectrum is interference from nearby wireless networks. For example, in the case of WPANs, such as WPANs that operate in accordance with the IEEE 802.15.3c standards, only a few channels are defined within in a limited bandwidth to support high data rate applications. The independent TDMA scheduling of service periods by each network may result in co-channel interference between the networks. Although the network devices can identify interference from neighboring networks and communicate during times that are free from interference, this process is time consuming and generally ineffective when the interference changes dynamically.

Thus, what are needed are wireless networks and methods that reduce the effects of interference from neighboring networks. What are also needed are methods of reducing the effects of co-channel interference in a WPAN operating in accordance with the IEEE 802.15.3c standards.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims.

FIG. 1illustrates a communication environment including nearby wireless networks in accordance with some embodiments. The communication environment illustrated inFIG. 1includes wireless network100and nearby wireless network110. Both wireless networks100and110may employ TDMA, such as WPANs, and may operate in accordance with the IEEE 802.15.3c standards, although the scope of the embodiments is not limited in this respect. In some embodiments, wireless network100and wireless network110may utilize the same unlicensed frequency spectrum, such as the 60 GHz unlicensed frequency spectrum, although the scope of the embodiments is not limited in this respect.

Wireless network100may include central controller102to coordinate the operations of wireless network100. Communication stations104, designated individually as communication station104A through104F, of wireless network100may be assigned channel-time allocations (CTAs)103within superframes for peer-to-peer communications with another communication station104. In addition to assigning time for communication between communication stations104, central controller102may support isochronous traffics, maintain network synchronization time, and perform admission control. This allows the wireless resource to be shared among communication stations104. In these embodiments, central controller102may assign a first CTA of a superframe for communication stations104A and104B to communicate, may assign a second CTA of the superframe for communication stations104C and104D to communicate, and may assign a third CTA of the superframe for communication stations104E and104F to communicate. Central controller102may also manage the QoS requirements of wireless network100.

Similarly, wireless network110may include central controller112to coordinate the operations of wireless network110. Communication stations114, designated individually as communication stations114A through114F, of wireless network110may also be assigned CTAs113within superframes for peer-to-peer communications with another communication station114of network110. In some embodiments, central controller112may assign a first CTA113of a superframe for communication stations114A and114B to communicate, may assign a second CTA113of the superframe for communication stations114C and114D to communicate, and may assign a third CTA113of the superframe for communication stations114E and114F to communicate.

This independent scheduling by wireless network100and wireless network110may result in interference between the communication stations of one network that are close to the communication stations of the other network since the networks share the same unlicensed frequency spectrum. For example, the communications of communication stations104A and104B of wireless network100may interfere or collide with the communications of communication stations114A and114B of wireless network110.

In accordance with embodiments, central controller102may randomize locations of the CTAs103within superframes to help avoid co-channel interference from one or more neighboring networks. In this way, the effect of interference from neighboring co-channel wireless networks is migrated by spreading interference across multiple superframes. In some embodiments, an interference estimation process may be utilized, although this is not a requirement. These embodiments are discussed in more detail below.

Central controller102of wireless network100may transmit information within beacon periods101to communication stations104to allow communication station104to determine the randomized locations of the CTAs103within a superframe. Central controller112of wireless network110may also transmit information within beacon periods111to communication stations114to allow communication stations114to determine the randomized locations of the CTAs113within a superframe, however there is no requirement that both wireless networks100and110randomized locations of their CTAs. These embodiments are discussed in more detail below.

Co-channel interference is particularly an issue in a dense networking environment with multiple networks nearby each other. Current channelization in the IEEE 802.15.3c standard for WPANs define only 3 to 4 channels using approximately 2 GHz bandwidth to support high data rate applications. Since communications between neighboring WPANs is not addressed, the small number of available channels and the independent TDMA scheduling of service periods results in interference between neighboring WPANs. This co-channel interference problem gets even worse when WPANs that are based on different standards (heterogeneous WPANs) coexist in the same vicinity. Although a WPAN can estimate interference from neighboring WPANs to find an interference-free period for communications, interference estimation is a time consuming process and is effective when traffic of the neighboring WPANs lasts for a relatively long period of time. Furthermore, interference estimation becomes inefficient when traffic of neighboring WPANs changes dynamically (e.g., variable bit rate (VBR) traffic such as compressed video) or when the slots used by a neighboring WPAN changes in response to interference from a third WPAN.

Although WPANs are used to convey information over relatively short distances, the scope of the embodiments is not limited in this respect as embodiments are equally applicable to networks that communicate over greater distances. Although some embodiments described herein with respect to WPANs, the scope of the embodiments is not limited in this respect as embodiments are applicable to almost any TDMA network that uses a centralized service period allocation scheme. In some embodiments, central controller102, as well as central controller112, may be a Pico-Net controller (PNC), although the scope of the embodiments is not limited in this respect.

FIG. 2illustrates functional block diagrams of a central controller and a communication station in accordance with some embodiments. Central controller202may be suitable for use as central controller102(FIG. 1) and/or central controller112(FIG. 1), and communication station204may be suitable for use as any of communications104(FIG. 1) and/or communication stations114(FIG. 1).

Central controller202may include transceiver216to receive and transmit information using one or more antennas201to communication stations within its network, such as communication station204. Central controller202may also include beacon generator214to generate signals for transmission within beacon periods101to communication stations within its network. Central controller202may also include CTA schedule randomizer212to randomize locations of CTAs within superframes.

CTA schedule randomizer212may provide a schedule of the locations of randomly allocated CTAs, although the scope of the embodiments is not limited in this respect. The schedule may be transmitted within one or more of beacon periods101for receipt by the communication stations of the network. CTA schedule randomizer212may alternatively use a randomization seed and the number of CTAs to be allocated within a superframe to determine a starting CTA within a superframe. The starting CTA may be provided in one of beacon periods101and the communication stations may determine the locations of the CTAs within a superframe based on the starting CTA. Alternatively, the randomization seed and number of CTAs may be provided in one of beacon periods101to allow the communication stations to determine the starting CTA. These embodiments are discussed in more detail below.

Communication station204may include transceiver226for receiving communications from central controller202within beacon periods101and for communicating with other communication of the network. Communication station224may also include frame generator224for generating frames for use in communicating with other communication stations of the network. The frames may comprise superframes which may include a number of CTAs, as described in more detail below. Communication station224may also include CTA schedule randomizer222which may generate a schedule for the locations of allocated CTAs as indicated by central controller202. Central controller202may provide a randomization seed and the number of CTAs for use by CTA schedule randomizer222. Alternatively, central controller202may provide a randomized schedule of CTAs. These embodiments are discussed in more detail below.

Antennas201used by central controller202may comprise one or more omnidirectional antennas to allow central controller202to communicate with several communication stations located in various directions with respect to central controller. Antennas201may comprise several directional antennas.

Antennas203used by communication station204may comprise one or more omnidirectional antennas. Alternatively, antennas203may comprise one or more directional antennas that may be receive communications from central controller202and may direct their communications toward another communication station. Beamforming, antenna steering and phased array type antennas may be used to provide increased directivity between pairs of communication stations, although the scope of the embodiments is not limited in this respect.

Although central controller202and communication station204are illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, application specific integrated circuits (ASICs), radio-frequency integrated circuits (RFICs) and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, these may refer to one or more processes operating on one or more processing elements. Central controller202and communication station204may include additional functional elements not illustrated.

FIG. 3illustrates CTA randomization in accordance with some embodiments. As illustrated inFIG. 3, wireless network100(FIG. 1), designated as WPAN1, may use superframes302for allocating CTAs304to communication stations104, and wireless network110(FIG. 1), designated as WPAN2, may use superframes312for allocating CTAs314to communication stations114. Each of superframes302may include beacon period306and several CTAs304, and each of superframes312may include beacon period316and several CTAs314.

Referring toFIGS. 1 through 3, in accordance with some embodiments, central controller102coordinates operations of wireless network100by allocating CTAs304for peer-to-peer communications between pairs of communication stations104. In these embodiments, central controller102may randomize locations of CTAs304within superframes302to mitigate co-channel interference from neighboring wireless networks, such as wireless network110. In these embodiments, the randomization of the locations of CTAs304within superframes302may help mitigate co-channel interference with nearby wireless networks. A nearby wireless network, such as wireless network110may or may not implement an interference mitigation technique. In some embodiments, central controller102may include CTA schedule randomizer212to randomize locations of the CTAs304within superframes302.

CTAs304may comprise one or more sequential time slots within superframes302. In some applications, CTAs304may be service periods (SPs) and superframes302may be beacon intervals, although the scope of the embodiments is not limited in this respect.

For wireless network100, as illustrated inFIG. 3, CTA1304may be assigned to communication stations104A and104B, CTA2304may be assigned to communication stations104C and104D, and CTA3304may be assigned to communication stations104E and104F. For wireless network110, as illustrated inFIG. 3, CTA1314may be assigned to communication stations114A and114B, CTA2314may be assigned to communication stations114C and114D, and CTA3314ma be assigned to communication stations114E and114F.

In accordance with some embodiments, central controller102may implement a basic randomization scheme. In these embodiments, central controller102may provide locations of randomly allocated CTAs304within beacon period306for receipt by communication stations104of wireless network100. Beacon period306may be an initial time period of superframes302and identifies the locations of CTAs304within a subsequent one or more of superframes302. The locations (i.e., the order) of CTAs304within one or more subsequent superframes302may be selected randomly by CTA schedule randomizer212of central controller102. In these embodiments, beacon period306may be transmitted by central controller102at the beginning of each of superframes302and the locations of the CTAs assigned to station-pairs (i.e.,104A and104B) are randomized in the next superframe. The locations of the CTAs304may be transmitted to each of the communication stations104operating under control of central controller102within beacon period306.

In accordance with some other embodiments, central controller102may generate and use a randomization seed for randomizing locations of CTAs304within one or more of superframes302. Central controller102may generate a randomization seed. A starting CTA within one of superframes302may be calculated based on the randomization seed. The starting CTA may correspond to a pseudorandom number calculated based on the seed value and a number of CTAs to be allocated in a next superframe using a modulo operation. CTAs304may be assigned in a predetermined order within the next superframe starting with the starting CTA.

In some embodiments, CTA schedule randomizer212may generate the randomization seed and calculate the starting CTA. When CTAs304are assigned in a predetermined order, the order may be sequential. For example, in these embodiments, if the starting CTA is CTA4, the CTAs may be assigned sequentially within the next superframe starting with CTA4and finishing with CTAs1-CTA3.

In some of these embodiments, central controller102may calculate the starting CTA for a superframe using the seed value and the number of CTAs using a modulo operation. In these embodiments, central controller102may provide an indication of the starting CTA to communication stations104in beacon period306and communication stations104may determine locations of CTAs304within a next of superframes302based at least on the indication of the starting CTA provided by central controller102. In these embodiments, central controller102may also provide an indication of the length (e.g., a number of time slots) of each CTA that will be allocated within the next superframe302. This may allow each of communication stations104to determine the location of each CTA within the next superframe. In these embodiments, CTAs304may be assigned in a predetermined order within the next starting with the starting CTA.

In some embodiments, the starting CTA may be calculated as follows:
Starting_CTA=random(seed,i) moduloN,

where random(seed, i) generates a pseudo-random number based on the value of the randomization seed at every iteration and N is the total number of CTAs in a super frame. Because these embodiments use a modulo operation, they are very efficient to implement.

Central controller102may provide the randomization seed, the number of CTAs to be allocated within the next superframe, and an indication of the length of each of the CTAs to communication stations104within beacon period306. Each communication station104may calculate the starting CTA for a next superframe using the seed value and the number of CTAs using a modulo operation. Communication stations104may determine the locations of CTAs304within next superframe302based in the indication of lengths provided by central controller102and the predetermined order. CTAs304may be assigned in a predetermined order within the next starting with the starting CTA. The randomization seed, the number of CTAs, and the indication of the length of each of the CTA may be transmitted within beacon period306to each of communication stations104operating under control of central controller102. In some embodiments, the predetermined order may be a sequential order beginning with the starting CTA. Each CTA may comprise one or more time slots. The number of time slots may correspond to the length of a CTA, although the scope of the embodiments is not limited in this respect.

For each superframe, each station may generate a pseudorandom number corresponding to the starting CTA based on the seed value and the number of CTAs to be allocated using a modulo operation. CTA schedule randomizer212may employ a random number generator which may be set to an initial state based on initial state information provided in the beacon period306. Communication stations104do not need to rely on information received in the prior beacon period306to determine the location of their assigned CTA in superframes following the next superframe302. Communication stations104may be configured to initialize or reset the random number generator prior to calculating the starting CTA.

The probability that two links will collide can be calculated as follows. Assuming that all the CTAs have the same time duration TCTAand assuming that the available time for CTA allocations in a superframe is TSF, due to beacon synchronization, the probability that two CTAs will conflict can be expressed as:
Pr(collision in a superframe)=pc=TCTA/TSF

The probability that there will be no collisions for n consecutive superframes can be expressed as:
Pr(no collisions fornconsecutive superframes)=(1−pc)n

As the duration of CTA decreases the collision probability decreases.

In some embodiments, central controller102may further randomize the CTAs304within a superframe by instructing communication stations104to cyclically rotate CTAs304from one superframe to a next superframe. These embodiments are discussed in more detail below.

FIG. 4illustrates cyclic shifting of time slots of CTAs in accordance with some alternate embodiments.FIG. 4illustrates a plurality of sequential superframes402, illustrated as402A,402B and402C. In these embodiments, central controller102may provide an indication in beacon period406that time-slots408of CTAs within superframe402are to be cyclically rotated from one superframe402A to a next superframe402B. In the embodiments illustrated inFIG. 4, times slots of a CTA remain contiguous in each superframe402. In these embodiments, communication stations104(FIG. 1) do not need to rely on information received in the prior beacon period406to determine the location of their assigned CTA in superframes following the next superframe402.

In some embodiments, co-channel interference estimation may not be necessary. Central controller102(FIG. 1) may refrain from performing interference estimation to detect co-channel interference with nearby wireless networks when central controller102(FIG. 1) is configured to randomize the locations of the CTAs within superframes402. Central controller102(FIG. 1) may instruct communication stations104(FIG. 1) within wireless network100(FIG. 1) to refrain from performing interference estimation when central controller102(FIG. 1) is to randomize the locations of CTAs within superframes402. In these embodiments, interference estimation under IEEE 802.15.3c may not be performed.

In some alternate embodiments, interference estimation may be performed by central controller102(FIG. 1) and/or communication stations104(FIG. 1) to detect co-channel interference and determine whether the detected co-channel interference is static or dynamic. These embodiments are discussed in more detail below.

FIG. 5Aillustrates interference estimation for TDMA networks in accordance with some embodiments with same-duration superframes.FIG. 5Billustrates interference estimation for TDMA networks in accordance with some embodiments with different-duration superframes.

As illustrated inFIGS. 5A and 5B, wireless network100(FIG. 1) is designated as WPAN1and may use superframes502, and wireless network110(FIG. 1) is designated as WPAN2, may use superframes512for allocating CTAs514to communication stations114. Each superframe502may include beacon period506, and each superframe512may include beacon period516and several CTAs514. As illustrated inFIGS. 5A and 5B, wireless network100may perform interference estimation during portions520of superframes502.

As illustrated inFIG. 5A, wireless network100(WPAN1) and wireless network110(WPAN2) may have superframes of the same duration. Wireless network100may detect interference522during CTA1of wireless network110. As illustrated, even though the superframes of the networks have the same duration, detected interference522does not necessarily repeat from superframe to superframe, nor does the detected interference522have the same length.

One reason that wireless network100detects interference522during CTA1of wireless network110is that CTA1is the service period that communication stations114A and114B communicate. As illustrated inFIG. 1, communication stations114A and114B are nearest central controller102and communication station104A and104B of wireless network100. CTA2and CTA3of wireless network110are less likely to cause interference.

As illustrated inFIG. 5B, wireless network100(WPAN1) and wireless network110(WPAN2) may have superframes of different durations. Wireless network100may detect interference522during CTA1of wireless network110. As illustrated, detected interference522may occur in different locations of superframes502

Detected interference522illustrated inFIGS. 5A and 5Bare examples of dynamic interference because it is not predictable and does not occur on a regular or repeating basis. In accordance with some embodiments, central controller102may perform an interference estimation to detect co-channel interference with nearby wireless networks110. When co-channel interference is detected from one or more neighboring wireless networks110, central controller102may analyze the detected interference to determine whether the detected co-channel interference is static or dynamic. When central controller102determines that detected co-channel interference is static, central controller102may refrain from randomizing the locations of CTAs within superframes as discussed above, and may assign the CTAs to portions of a next superframe where the static co-channel interference is predicted not to be present. In these embodiments, static co-channel interference may be co-channel interference that is determined to occur on a regular or repeating basis (i.e., every so many seconds) allowing its time location in the near future to be predicted.

In these embodiments, when central controller102determines that the detected co-channel interference is dynamic, central controller102may inform the communication stations104that the locations of the CTAs are to be randomized within the superframes302in accordance with one of the embodiments discussed above. For example, the central controller102may provide the randomized locations of the CTAs to the communication stations104in beacon period306, use a randomization seed to determine a starting CTA, or provide the randomization seed to the communication stations104in a beacon period306to allow the communication stations to determine the starting CTA. In these embodiments, dynamic co-channel interference522may be co-channel interference that does not occur on a regular or repeating basis (e.g., its location in the next superframe is unpredictable).

In some embodiments, communication stations104may perform an interference detection process to detect co-channel interference from one or more neighboring wireless networks110. When communication stations104detect co-channel interference, the communication stations104may report the detected co-channel interference to central controller102. Superframes302may include a contention access period not separately illustrated which may be used by communication station104to request assignment of CTAs as well as to report detected co-channel interference, although the scope of the embodiments is not limited in this respect. In some embodiments, central controller102may also or alternatively be configured to detect co-channel interference from one or more neighboring wireless networks.

Unless specifically stated otherwise, terms such as processing, computing, calculating, determining, displaying, or the like, may refer to an action and/or process of one or more processing or computing systems or similar devices that may manipulate and transform data represented as physical (e.g., electronic) quantities within a processing system's registers and memory into other data similarly represented as physical quantities within the processing system's registers or memories, or other such information storage, transmission or display devices. Furthermore, as used herein, a computing device includes one or more processing elements coupled with computer-readable memory that may be volatile or non-volatile memory or a combination thereof.

Embodiments may be implemented in one or a combination of hardware, firmware and software. Embodiments may also be implemented as instructions stored on a computer-readable medium, which may be read and executed by at least one processor to perform the operations described herein. A computer-readable medium may include any tangible medium for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a computer-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and others.