WO2010059033A2

WO2010059033A2 - Seamless data rate adaptation in a wireless communication network

Info

Publication number: WO2010059033A2
Application number: PCT/MY2009/000197
Authority: WO
Inventors: Rashid Abdelhaleem Saeed; Hafizal Mohamad; Borhanuddin Mohd Ali
Original assignee: Mimos Berhad
Priority date: 2008-11-20
Filing date: 2009-11-19
Publication date: 2010-05-27
Also published as: MY151542A; WO2010059033A3

Abstract

A method for controlling data transmission rate in a wireless network, the method comprising the steps of providing information of the interference margin (30) to a base station (12) by each active link, receiving a bandwidth allocation request (19) at one node, measuring a channel quality (20) for the node, and determining (21) a need to assign a power level and rate based on the information of the channel quality (20) of the node and the interference margin obtained (30) from the base station (12).

Description

Seamless Data Rate Adaptation in a Wireless Communication

Network

Field of Invention

The present invention relates generally to network communications and more particularly to a method for controlling data transmission rate in a wireless network.

Background of the Invention

At present, there is one prominent standard or mode of operation with respect to the advent of wireless network which is Worldwide Interoperability for Microwave Access (WiMAX) which deploys the Institute for Electronic and Electrical Engineers (IEEE) 802.16 standard. WiMAX is supported by wireless wide area network (WWAN) communication technique for mobility (IEEE 802.16e) or stationary (IEEE802.16d) users. The primary beneficial divergence of WiMAX is the capability to provide elevated flexibility in implementations whilst maintaining considerable level of data rate as well as transmission range.

IEEE 802.16 Wireless MAN (Metropolitan Area Network) has a connection-oriented medium access control (MAC) and physical

(PHY) is based on non-line-of-sight (NLOS) radio operation in 2-11 GHz. For licensed bands, channel bandwidth shall be limited to the regulatory provisioned bandwidth divided by any power of 2, no less than 1.25MHz. Mobile WiMAX which is one of the WiMAX IEEE 802.16 technologies that serve this market can provide internet access to mobile platforms using an extension of the WLAN technology.

Orthogonal frequency division multiple access (OFDMA) is an enhancement to existing OFDM technology. This technology divides a signal into sub-channels for example groups of carriers, with each sub-channel being allocated to a different subscriber. The present mobile-WiMAX invention employs OFDMA PHY layer and MAC layer specification based on IEEE 802.16e standard for licensed bands to enable the operation of nodes with low speeds. The standard is amended as well for multihop IEEE 802.16j to enable relay stations (RSs) for coverage extend and data rate enhancement. WiMAX link adaptation constitutes efficient means to enhance throughput and increase transmission reliability of wireless communication networks.

The aim of the present invention is to provide seamless rate adaptation technique in order to improve energy efficiency by minimizing the total transmission power over transmission data rates, subject to the traffic requirements of all the nodes in the multi-hop network. A IEEE 802.16j is a tree topology network which is also known as a multi-hop network allows for connection by hopping from node to node until the destination is reached.

These and other advantages will become apparent to those skilled in this art from the following detailed description of illustrative embodiments thereof, which is to be read in conjunction with the accompanying drawings.

Summary of -the Invention

In the present invention, a method for controlling data transmission rate in a wireless network, the method comprising the steps of providing information of the interference margin to a base station by each active link, receiving a bandwidth allocation request at one node, measuring a channel quality for the node, and determining a need to assign a power level and rate based on the information of the channel quality of the node and the interference margin obtained from the base station.

In accordance to the present invention, channel quality for the node includes measurements of interference and noise levels .

In accordance to the present invention, the step of determining a need to assign a power level and rate includes the steps of determining its own interference margin is nonnegative, and determining the interference to any other existing active link does not exceed its interference margin.

Brief Description of -the Drawings

Other objects, features, and advantages of the invention will be apparent from the following description when read with reference to the accompanying drawings. In the drawings, wherein like reference numerals denote corresponding parts throughout the several views:

Fig. 1 shows the two scenarios supported by IEEE802.16e for mobile and fixed nodes. The mobile nodes are suffering from deterioration of data rate due to Doppler shift when the vehicular speed is increasing;

Fig. 2 depicts an illustration of the problem statement of the effect of mobile speed without rate adaptation, which the illustration shows that the link account high delay for synchronization and also the link may goes down due to the high speed.

Fig. 3 illustrates a method for controlling data transmission rate in a wireless network with the rate adaptation technique incorporated into the system of the present invention; Fig. 4 is a graph of the throughput versus number of packets for comparison between a standard and seamless rate adaptation of the present invention; and

Fig. 5 is a graph of the dropped packets versus bandwidth for comparison between a standard and seamless rate adaptation of the present invention.

Detailed Description of the Preferred Embodiments

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known methods, procedures and/or components have not been described in detail so as not to obscure the invention. Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

The present invention will be described herein in the context of an IEEE 802.16 compliant orthogonal frequency division multiple access (OFDMA) wireless communication system. It should be appreciated, however, that the present invention is not limited to this or any particular wireless communication system. Rather, the invention is more generally applicable to techniques for more optimally controlling a data transmission rate in a wireless system. Also, although particularly well- suited for use in conjunction with the IEEE 802.16j standard, the invention can be used with other standards, as well as in non-standard systems.

The purpose of IEEE proposal for mobiIe-WiMAX multihop relay is to enhance coverage, throughput and system capacity of 802.16e networks by specifying 802.16j multihop relay capabilities and functionalities having interoperable relay stations (11) and base stations (12). However, the mobile station (13) with high speed about 60km/hr of vehicular speed will suffer from frequency-selective fading and Doppler shift. Consequently, the achievable data rate could be less than IMbps. Therefore, there is an opportunity to provide an effective rate adaptation technique to combat predicament caused by high speed mobility effects and also to increase the mobile data rate approximately up to 50 percent. Fig. 1 shows the deterioration of data rate due to Doppler shift while the vehicular speed is increasing.

Mobile Multihop Relay Base Station (12) refers to a base station that is compliant with amendments IEEE 802.16j through IEEE 802.16e, which has extended functionality to support MMR as defined in 802.16j. The invention provides a rate adaptation technique to reduce loss of data rate when mobility is increased and thus enhances the overall system performance. In mobile-WiMAX technology, when the mobile station (MS) (13) speed increases for example in the range of lOkm/hr to 60km/hr, the wireless transmission channel will be influenced by Doppler shift, frequency- selective fading and interference due to channel impulse response fluctuation. Any interference on the connection can cause the relay station (RS) (11) drops the existing connection and to retrain on another connection. In a wireless communication network, Doppler shift occurs when the distance between a transmitting platform and a receiving platform differs .

The mobile station (13) and the base station (12) waste their resources to compensate the bit errors due to Doppler shift and frequency selective fading which lead to decrease the mobile station (13) bandwidth or data rate. Bandwidth is the number of bytes that can cross the link per second while throughput is the average number of bytes that cross the central link in a second. The resources impact varies widely, approximately from 50% up to 90% of the available bandwidth to keep bit error rate up to 10^"3.

In order to allocate rate resources in WiMAX, the system-level information exchange usually imposes heavy signaling overhead and a central controller which may be a selected node is necessary to broadcast synchronization information (14), collect the traffic request of every node and status of every link (15), and determine active links with the allowed power levels, their transmission time duration, and transmission rates .

A suboptimal power or rate allocation scheme using seamless rate adaptation is used in the present mobile-WiMAX networks. After the power or rate allocation is performed locally a distributed scheme can be adopted, in which each node performs admission decision for each request and determines the transmission power and rate if the request is admitted, based on channel quality information channel (CQICH) measurements of the mobile station (13) and information obtained from the base station (12) . Fig. 2 shows a reduction in cycle time when the rate adaptation process is implemented to the system.

In order to avoid frequent rate reconfiguration after each new request is admitted, each link keeps a maximum sustainable interference (MSI), which is also referred to as the interference margin. The MSI denotes the additional tolerable interference while not violating the signal-to-interference- plus-noise ratio (SINR) requirement, i.e., for link i, ^r IbIJ

SINR = 5

Ri (ηi + T_f∑ P_kgkj(t) + MSI₁) k=l k≠ i k≠j

where Pi denotes the average transmission power of link i's

transmitter, R± the bit rate of link i, //,^■ the background noise

energy plus non- UWB interference energy, and Tf the pulse repetition time. The equation (1) is then leads to

MSI₁ = -^ η, - T_f YP_kg. (t) (2)

' SINR.R, '' ^ftt k≠i k≠j

The MSI values of all the links are updated upon each new link admission and should be nonnegative in order to keep the transmission accuracy of all the links.

Fig. 3 shows an exemplary sequence of steps for implementing the seamless rate adaptation in accordance with the present invention. When the mobile station (13) speed increases, the mobile station will synchronize (16) with downlink and obtain the downlink and uplink connection. The mobile station (13) will then request (17) for new rate assignment. The base station (12) receives (18) CDMA codes that request for a ranging process and therefore bandwidth request message (19) will be forwarded and the system will perforin the measurement (20) of the channel quality using CQICH message of the mobile station (13) .

Each active link periodically announces it MSI value over a control channel (30) . When a new call request for a new link arrives at one node, according to local measurements of interference and noise levels, and MSI information of other links, the node determines whether it is feasible to have an assigned power level and a rate such that its own MSI is nonnegative, and the interference due to the new transmission if admitted, to any other existing active link does not exceed its MSI.

For multiple accesses in a multi-channel environment, each active link periodically announces its MSI value over a control channel. If a link's MSI is honored by all the other links, its transmission rate can be guaranteed. Consider a UWB network with N active flows with rate requirement from Ri to R_n. Upon a new transmission flow request i with required rate Ri, the procedure which shows two steps namely a first step is to guarantee that the MSIs of all the existing flows are honoured, while the second step is to guarantee that a newly admitted flow can obtain a nonnegative MSI. The transmission power Pi of link i is calculated (21) and should be constrained by the MSIs of existing active links, i.e.,

If the bit error rate (BER) equal or lesser than ε (22) , where ε value is based on the path-loss models in the standard indoor pedestrian or vehicular and Pi = 0 (23) , data will be sent (24) as the new rate is feasible. However, if Pi > 0 (25), the system will reject the flow request (26) and drop the current packet.

Fig. 4 shows a graph for the relation of throughput vs. number of packets for comparison between standard (27) and seamless (28) rate adaptation. It is observed that with the present seamless rate adaptation technique incorporated into the system, it has significantly enhanced the throughput of the system. Fig. 5 shows a graph for the relation of dropped packets versus bandwidth for comparison between standard (27) and seamless (28) rate adaptation. The number of dropped packets decreases as the bandwidth increases. When the data rate goes less than IMbps due the Doppler shift, the number of dropped packets is at its highest rate. It is also shown that with the present seamless rate adaptation technique incorporated into the system, the rate of the dropped packets as the bandwidth increases has been reduced. It should be noted that as the bandwidth approaches and exceeds lOMbps, the rate of decreases in the percent of dropped packets lessens.

As will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its essential characteristics. The present embodiments is, therefore, to be considered as merely illustrative and not restrictive, the scope of the invention being indicated by the claims rather than the foregoing description, and all changes which come within therefore intended to be embraced therein.

Claims

1. A method for controlling data transmission rate in a wireless network, said method comprising the steps of: providing (30) information of the interference margin to a base station (12) by each active link; receiving a bandwidth allocation request (19) at one node; measuring a channel quality (20) for said node; and determining (21) a need to assign a power level and rate based on the information of said channel quality (20) of said node and said interference margin (30) obtained from said base station (12) .

2. The method for controlling data transmission rate in a wireless network as claimed in claim 1, wherein said step of measuring a channel quality (20) for said node includes measurements of interference and noise levels.

3. The method for controlling data transmission rate in a wireless network as claimed in claim 1, wherein said step of determining (21) a need to assign a power level and rate includes the steps of: determining its own interference margin is nonnegative; and determining the interference to any other existing active link does not exceed its interference margin.

4. The method for controlling data transmission rate in a wireless network as claimed in claim 3, wherein said interference margin is maximum sustainable interference (MSI) value.

5. The method for controlling data transmission rate in a wireless network as claimed in claim 1, wherein said bandwidth allocation request (19) is sent by a mobile station (13) with high vehicular speed.

6. The method for controlling data transmission rate in a wireless network as claimed in claim 5, wherein said mobile station (13) has a high speed approximately 60km/hr.

7. The method for controlling data transmission rate in a wireless network as claimed in claim 1, wherein said base station (12) is a mobile-WiMAX multihop relay base station.

8. The method for controlling data transmission rate in a wireless network as claimed in claim 7, wherein said base station (12) is compliant with orthogonal frequency division multiple access (OFDMA) wireless communication system standard under 802.16j .