DESC:FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

Title: A METHOD OF ROAMING IN A MULTI NETWORK WIRELESS COMMUNICATION SYSTEM

APPLICANT DETAILS:
(a) NAME: Bharat Electronics Limited
(b) NATIONALITY: Indian
(c) ADDRESS: Outer Ring Road, Nagavara, Bangalore - 560045. Karnataka, India

PREAMBLE TO THE DESCRIPTION:
The following specification (particularly) describes the nature of the invention (and the manner in which it is to be performed):
A METHOD OF ROAMING IN A MULTI NETWORK WIRELESS COMMUNICATION SYSTEM

FIELD OF INVENTION:
The present disclosure relates to the field of wireless radio networks. Specifically, the present disclosure relates to a method of roaming in a multi network wireless communication system.

BACKGROUND OF THE INVENTION:
The following background discussion includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication expressly or implicitly referenced is prior art.
There are different kinds of wireless radio networks, one is infrastructure-based network, and the second one is infrastructure-less networks. Examples of infrastructure-based networks are cellular, Wi-Fi, Professional mobile radio (PMR) and satellite networks. Examples of infrastructure-less networks are MANETs and Wireless sensor Networks (WSNs).
US patent No: US 8,045,982 B2 relates to a method for Site selection for a multi-site communication system. In this a device detects a first signal on a channel that is one of a plurality of channels arranged in a first order on a list, with each channel being associated with a different site in a multisite communication system. Upon detecting the first signal, the device attempts to measure and record signal strength of a signal at each channel on the list based on the first order beginning with the detected first signal and selects as a home site the site associated with the channel having the signal with the highest recorded signal strength. The device rearranges the channels on the list into a second order based on the recorded signal strengths with the home site channel at the top. If necessary, the radio attempts to awaken its repeaters one after another based on the second order until a repeater is found to transmit a signal.
Another US patent No: US 8,675.480 B2 titled “Communications system providing enhanced channel switching features based upon modulation fidelity and related methods”. It uses modulation fidelity value wherein the received modulation differs from transmitted modulation value. The base station and the communications device are configured to determine respective modulation fidelity values associated with a current channel and an alternate channel based upon an estimated modulation fidelity calculated from the received modulation, and to selectively switch between the current channel and the alternate channel based upon the determined modulation fidelity value.
As a user roams in a multi network communication system, the user may move from one coverage area served by one base station to a new coverage area served by a different base station. In this case, the radio must be able to detect the base station in the new coverage area to facilitate communications in that coverage area.
A manual approach to find the new base station involves manual tuning of radio to a different channel to locate the base station for the coverage area where he is currently present. However, this approach is time-consuming and not an effective way to find the base station, which provides connectivity to the rest of the network.
However, there is a need of a method of roaming in a multi network wireless communication system for automatic switching of base station without the intervention of the user for the seamless communication based on the connectivity with base station and periodic transmission of beacon packets containing SYNC data in the respective coverage area of a base station and also immune to momentary link failures due to unreliable nature of wireless links.

OBJECTIVES OF THE INVENTION:
The primary object of the present invention is to overcome the problem stated in the prior art.
Another object of the present invention is to provide a method of roaming in a multi network wireless communication system for automatic switching of base station without the intervention of the user for the seamless communication based on the connectivity with base station and periodic transmission of beacon packets containing SYNC data in the respective coverage area of a base station and also immune to momentary link failures due to unreliable nature of wireless links.
SUMMARY OF THE INVENTION:
In an aspect, present invention provides a method of roaming in a multi network wireless communication system comprising steps of:
a) transmitting beacon packet periodically for every time period T1 when there is no other active voice/message transmission by a base station; and
b) connecting a mobile station to the base station as long as it receives beacon packet or voice/message reception continuously from the base station;
where the said mobile station doesn’t shift to scan mode abruptly based on the random misses of beacon packet due to uncertain nature of wireless channel where the base station transmits beacon packet periodically for every period T1.
In an embodiment, when said mobile station misses two consecutive beacon packets, it sends a probe packet to the current base station.
In an embodiment, the said mobile station remains connected to the current base station if it receives the response for the probe packet.
In an embodiment, the mobile station switched the channel to the next channel as per the roam list when probe packet response is not received.

DETAILED DESCRIPTION OF DRAWINGS:
To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of their scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings in which:

Fig. 1: illustrates a illustrates multiple base stations and their respective coverage areas, each base station operates at different channel with different Rx and Tx frequencies.
Fig. 2: illustrates a state diagram for a mobile station.
Fig. 3: illustrates a block diagram of base station unit.
Fig. 4: illustrates a roaming list of mobile station unit.

DETAILED DESCRIPTION:
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
The terms “comprises”, “comprising”, “includes”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or method.
The present invention provides a method of roaming in a multi network wireless communication system for automatic switching of base station without the intervention of the user for seamless communication.

In an aspect, present invention provides a method of roaming in a multi network wireless communication system comprising steps of:
a) transmitting beacon packet periodically for every time period T1 when there is no other active voice/message transmission by a base station; and
b) connecting a mobile station to the base station as long as it receives beacon packet or voice/message reception continuously from the base station;
where the said mobile station doesn’t shift to scan mode abruptly based on the random misses of beacon packet due to uncertain nature of wireless channel where the base station transmits beacon packet periodically for every period T1.
In an embodiment, when said mobile station misses two consecutive beacon packets, it sends a probe packet to the current base station.
In an embodiment, the said mobile station remains connected to the current base station if it receives the response for the probe packet.
In an embodiment, the mobile station switched the channel to the next channel as per the roam list when probe packet response is not received.
Figure 1 illustrates multiple base stations and their respective coverage areas; each base station operates at different channel with different Rx and Tx frequencies. Figure 2 illustrates the state diagram for a mobile station, initially a mobile station is bound to a particular base station and continue so as long as it receives beacon packets from it. When it misses two consecutive beacon packets, it tries to find the presence of the Base station by sending a probe packet, if it doesn’t get the reply for a probe packet, it switches to the next channel being serviced by a different base station. Figure 3 illustrates the block diagram of base station unit. It consists of separate modules for Rx chain and Tx chain and a control module for call processing and dispatcher activities. Figure 4 illustrates the roaming list of mobile station unit. It consists of a base stations list with corresponding Tx and Rx frequency information.
The present method of invention is implemented and tested over indigenous handheld radios and base station.
In this method of invention multiple Base stations are installed over a geographic location to provide communication services like voice and short message within the coverage area of respective base station. Each Base station operates in a separate channel and list of channels are represented in a roam list table (Fig-4). As the users move around the coverage area they may lose the connectivity with their current base station and move to the coverage area of a neighboring base station.
A base station is a communication device which is part of fixed infrastructure and can communicate in full duplex mode, it can receive either voice or data from a radio and transmits the same voice/data to one or more radios simultaneously. It also maintains the list of mobile stations currently being serviced. For the base station Tx frequency is denoted by F1 and Rx frequency is denoted by F2 and both frequencies supposed to be different, so the base station shall receive and transmit simultaneously.
Whereas for the mobile station F2 becomes the Tx frequency and F1 becomes the Rx frequency, so that it can communicate seamlessly with the base station.
In prior art No.1, it employs a passive method of signal detection to find the base station, this method may not be efficient at some times when there is no transmission from base station for extended periods of silence. So, it takes longer time for switching in some cases.
In prior art No.2, it also employs a passive method of base station identification for switching. It uses modulation fidelity value of the received signal at mobile station, associated with a current channel and an alternate channel, and to selectively switch between the current channel and the alternate channel based upon the determined modulation fidelity value. This method involves overheads for calculating modulation fidelity value. This method also may take longer time for switching, when there are no transmissions from the base station.
Each base station transmits beacon packet periodically for every time period T seconds, beacon packet contains the SYNC data as well as the base station identity information. Whereas the mobile stations that are in the coverage area of the base station receive the beacon packet and remain connected to the base station as long as it receives beacon packets continuously.
An active mobile station doesn’t shift to scan mode abruptly based on the random misses of beacon packet due to uncertain nature of wireless channel. where in when the mobile station misses two consecutive beacon packets, then on it sends a probe packet to the current base station to check whether it can reach it. If the mobile station is able to receive the response for the probe packet, then it remains connected to the base station and there shall not be any switching of the channel to the next base station.
In case the mobile station does not receive any response for the probe packet then only it switches to next available channel as per the roam list, and the same process continues till it identifies a base station.
With the beacon time interval T seconds, it takes 3*T seconds to switch to the next base station in best case and 3*T + T*(N-1) seconds in worst-case scenario. Different values for T like 30, 20 and 10 seconds are experimented, and 10 seconds interval is observed to be better with switching time of 30 seconds with 2 base stations. Further, the interval time T may be reduced based on the requirements of the system and deployment scenario. A Base station shall send beacon packet only if there is no active transmission during the beacon interval of T seconds.
The base station described in the present embodiment is connected to other base stations through a fixed wired network. It maintains the list of mobile stations currently connected to it and other base stations also. It supports call forwarding and call routing of voice calls where the destination mobile station is connected to a remote base station. It also supports real time display of mobile stations on a GIS system for live tracking, based on GPS co-ordinates shared from mobile stations.
The present method of roaming in a multi network wireless communication system comprises of beacon exchanges and link procedures for base station selection in a multi network communication system. The said base station transmits beacon packet periodically for every time period T1 when there is no other active voice/message transmission. The said mobile station remains connected to a mobile station as long as it receives beacon packet or voice/message reception continuously. The said mobile station doesn’t shift to scan mode abruptly based on the random misses of beacon packet due to uncertain nature of wireless channel. The said mobile station misses two consecutive beacon packets, it sends a probe packet to the current base station. The said mobile station remains connected to the current base station if it receives the response for the probe packet. The said mobile station switched the channel to next channel as per the roam list.
The advantageous aspect of the present invention includes:
a. Automatic switching of channel of a mobile terminal in a multi network wireless communication system based on the connectivity with base station.
b. Periodic transmission of beacon packets containing SYNC data in the respective coverage area of a base station
c. Immune to momentary link failures due to unreliable nature of wireless links
The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the invention.

,CLAIMS:We Claim:

1. A method of roaming in a multi network wireless communication system comprising steps of:
a) transmitting beacon packet periodically for every time period T1 when there is no other active voice/message transmission by a base station; and
b) connecting a mobile station to the base station as long as it receives beacon packet or voice/message reception continuously from the base station;
where the said mobile station doesn’t shift to scan mode abruptly based on the random misses of beacon packet due to uncertain nature of wireless channel where the base station transmits beacon packet periodically for every period T1.
2. The method of roaming in a multi network wireless communication system as claimed in claim 1, wherein when said mobile station misses two consecutive beacon packets, it sends a probe packet to the current base station.
3. The method of roaming in a multi network wireless communication system as claimed in claim 1, wherein the said mobile station remains connected to the current base station if it receives the response for the probe packet.
4. The method of roaming in a multi network wireless communication system as claimed in claim 1, wherein said mobile station switched the channel to next channel as per the roam list when probe packet response is not received.