A Statistical Analysis of WiMAX Patents

( 1 May 2008 )

By Dr. S. Jagannathan (Tata Elxsi Ltd), Dr. T.K. Bandyopadhyay (Indian Institute of Technology), and Madhurjya Thakur (Patent Office Kolkata)

The IEEE 802.16 standards aim to consolidate the concept of Wireless Metropolitan Area Networks (WMANs). To bring this about, it is necessary to have high transmission rates across a large area for a large number of users. Worldwide Interoperability for Microwave Access (WiMAX) is the technology that enables this. Demand for wireless broadband access is growing fast, embracing an ever-widening range of applications: fixed, nomadic, portable and mobile data access, fixed and mobile voice services, and content streaming. WiMAX is committed towards meeting the requirements of all these applications through providing a robust and enhanced architecture that delivers real time voice, video, fax, and integrated data intercommunications.

A technology worthy of being commercialized, WiMAX also deserves to be protected as intellectual property (IP). A plethora of industry participants are presently involved in creating and exploiting WiMAX technology. Interestingly enough, there is as yet no comprehensive study on WiMAX technology and WiMAX patents. This paper makes a statistical analysis of WiMAX patents obtained by various industry participants.

PATENT ANALYSIS
WiMAX's underlying technical infrastructure relies heavily on a range of hardware and software devices and network technologies. The essential tools and elements that constitute WiMAX so often require intellectual property protection. The intellectual property regime (IPR) perspective of WiMAX has two key dimensions: IPR protection associated with the technology sector, and IPR licensing and/or assignments, covering royalty and profit sharing issues.

With the advent of new wireless technologies, patents, copyrights, designs and trademarks, and other intellectual property sectors will see tremendous impact on IPR protection, enforcement and infringement. Both technical and non-technical IPRs are, therefore, important in this field. The agencies involved have framed their own IPR policy. Even so, the global IPR protection scenario is still very much territorial in nature, and IPR enforcement/infringement are governed by the law of the states concerned. Cross border IPR infringements and litigation issues could result. It is important that stakeholders have an in-depth understanding of the impact of IPR. This paper represents an attempt in this direction.

PATENTS' CONTRIBUTION TO WIMAX FUNCTIONALITIES
Orthogonal frequency-division multiplexing (OFDM)
OFDM is a multi-carrier modulation technique that uses data symbols to modulate a parallel collection of regularly spaced sub-carriers. To maintain orthogonality, the sub-carriers must have minimum frequency separation, that is, the product of the symbol duration and the frequency separation of two consecutive sub-carriers must be unity (TxΔf=1), where "T" and "Δf" are called the symbol duration and sub-channel space of OFDM, respectively. OFDM is simple to use on channels that exhibit time delay spread or frequency-selectivity. Frequency-selective channels are characterized by their delay spread.

Companies working on OFDMA include: Qualcomm Inc., with 150 patents on OFDM/OFDMA; MakSat; Matsushita Electric Ind. Co. Ltd; Adaptix Inc., with two patents; Sharp Laboratories of America Inc.; and Wi-LAN Inc. The following are some companies/institutions and the patents they hold: Ensemble Communications, patent numbers 6,693,887, 6,683,866, 6,577,863, and 6,549,759; Wi-LAN, 7,197,022, 7,177,598, 7,023,798, 7,006,530, 6,956,834, 6,944,188, 6,925,068, 6,804,211, and 6,728,514; and University of Bristol, 6,963,617.

Reed-Solomon codes
Reed-Solomon codes are a class of linear, nonbinary, cyclic block codes. This class is a subfamily of the linear, non-binary, cyclic BCH code, which operates over the Galois field GF (q) of binary BCH codes, where q is a power of a prime number p prime, q = p^m prime, and m is a positive integer. These codes are different from binary codes, which have elements taken from the binary field GF (2).
c(x) = m(x)x^n-k -Rg(x)[m(x)^xn-k]

Where:
c(x) is the code word polynomial (output of RS encoder);
m(x) is the polynomial input to the RS encoder;
Rg(x)[y] denotes the operation of taking the remainder after dividing "y" by "g(x)";
g(x) is the generator polynomial.

Reed-Solomon decoder
The Reed-Solomon code follows the general steps below:
- Computation of the syndrome
- Determination of an error locator polynomial using Berlekamp-Massey algorithm
- Identifying the roots of the error locator polynomial using Chien search
- Determination of error values using Forney's algorithm

Among the companies working on error correction codes are 4i2i Communications Ltd, Actel Corp. and Altera Corp. Meanwhile, the following are companies holding patents on this technology: Analog Devices, AT&T Wireless Services, and Mitsubishi Electric.

Convolutional encoder and Viterbi decoder
The information bits do not flow through directly into the code-stream, that is, the code is not systematic. Non-systematic codes give better performance than systematic codes when Viterbi decoding is used. The encoder works by adding modulo-2 input bit to stored values of previous input bits to form outputs, which are buffered ready-for-transmission. The input bit is then moved into shift registers, and all other bits shift towards the output.

The Viterbi algorithm (VA) performs the maximum likelihood-decoding. It is applied to the trellis of a convolutional code whose properties are conveniently used to implement this algorithm. A key problem that faces maximum likelihood decoding is the number of calculations that need to be performed over all possible code sequences. The VA reduces the complexity of calculation by avoiding taking into account all possible sequences. The decoding procedure consists of calculating the hamming distance between the received sequences at an instant t_i at a given state of the trellis, and each of all code sequences that arrive at that state at that instant t_i.

This calculation is performed for all states of the trellis and for successive time instants with a view to identify the sequence with the minimum hamming distance. The sequence with the minimum hamming distance is the sequence with the highest probability of being identical with the received sequence when transmission is done over the AWGN channel.

One of the notable companies working on convolutional encoder and Viterbi decoder is Lattice Semiconductor Corp. Meanwhile, the following are companies holding patents on convolutional encoder and Viterbi decoder: Paradyne, General Instrument Corp. of Delaware, Qualcomm and Daewoo Electronics.

Interleaver
Interleaving is a widely used technique in digital communication. An interleaver takes a given sequence of symbols and permutes their positions, arranging them in a different order. The basic goal of an interleaver is to randomize the data sequence. When used against burst errors, interleavers are designed to convert error patterns that contain long sequences of serial erroneous data into a more random error pattern, thus distributing errors among many code vectors.

mQpsk modulation
The carrier undergoes four phase (symbol) changes and can represent 2 binary bits of data per symbol. Though initially, this might seem insignificant, a modulation scheme is deemed to be one that can enable a carrier to transmit 2 bits of information instead of 1, thus effectively doubling carrier bandwidth. Multiplying the received signal by a sine wave of equal frequency will demodulate the phase shifts into frequency-independent voltage levels.

Ranging
The above-mentioned patents discuss a method for performing a ranging process between a basestation (BS) and a mobile station (MS) in sleep mode in a wireless access system. The BS provides the MS with an initial notification of a periodic ranging time that occurs during a sleep time interval, and during this sleep time interval the MS performs the ranging process. The initial notification is included in the first message, which indicates if the MS should terminate sleep mode to receive DL data. In this, the BS provides the MS with subsequent notifications of periodic ranging times that occur during the sleep time interval. The second message is transmitted to the MS as part of the ranging process such that MS performs a plurality of ranging processes within the sleep time interval.

The ranging method for an access terminal requests ranging from an access point through a wireless network and performs the ranging according to the response from the access point.

MAC management
MAC management covers the management of MAC messages, which support dynamic resources reservation for upstream data traffic in a broadband cable system.

Uplink and downlink map messages (UL-MAP/DL-MAP)
An access terminal receives and analyzes UL-MAP/DL-MAP, and further:
- selects a given uplink sub-channel number and a symbol number from the UL-MAP when a ranging event is generated;
- requests a ranging process by transmitting a CDMA code;
- receives a ranging response message broadcast from the access point;
- extracts a CDMA code, a sub channel number, and a symbol number from the received ranging response message; compares the extracted result and the stored ranging parameters; adjusts transmission power, timing, and frequency offset based on the extracted result or by discarding the ranging response message;
- terminates a ranging response message receipt operation.

CONCLUSION
The WiMAX IP space is set to expand in line with the demand for wireless broadband access, including fixed, nomadic, portable and mobile data access, fixed and mobile voice services, and content streaming across a plethora of applications.

REFERENCES
Technical specifications white paper release, "Broadband Radio Access Networks (BRAN) HiperMan Physical (PHY) layer", WiMAX Forum

Technical specifications white paper release, "OFDM Processing Survey", WiMAX Forum

Communication Block Set for use with Simulink, The Mathworks Inc.

Learning Simulink6, The Mathworks Inc.

IEEE Communication Magazine, Vol. 43 No. 1, 2, January 2005

IEEE Networks Magazine, Vol. 27 No. 2, January 2005

Andreas F. Molisch, "Wireless Digital Communication", Second Edition, Pearson Education

IEEE Wireless Communication Magazine, Vol. 43 No. 1, January 2005

Scientific American Journal, Vol. 25 No. 6, March 2004


CAPTIONS:
Figure 1: Statistics of recent patents covering physical layer functionalities.

Figure 2: Statistics of recent patents covering MAC layer functionalities.

Click here for Illustrations:

Figure 1, Figure 2