 Hello, welcome to another module in wireless communications in this MOOC massive open online course. So far we have looked at a brief introduction to wireless communications, the 2G standard and 3G standard that is WCDMA. Let us talk briefly a little bit about another 4G or the 4th generation mobile wireless standard that is YMAX. And YMAX stands for Worldwide Interoperability for Microwave Access. The technical name for it is 802.16 and this group was formed in 1998 to develop an air interface for broadband wireless application that is really increase the wireless data rates to what you have on the Ethernet kind of broadband networks. And it was initially they have intended only for a line of site such as for instance where you have a very good signal strength between devices. And this original standardization was completed in 2001 and this was again evolved subsequently for instance 802.16 group subsequently produced 802.16A which is based on a novel technology known as OFDM or Orthogonal Frequency Division Multiplexing. This is an interesting standard, a very robust standard which we are going to see is forms the basis for a large number of 4G wireless standards because it supports a very high data rate. So that was extended to OFDM and the initial solutions in YMAX or 802.16 were fixed that is there was no mobility and they were known as fixed YMAX. And later around mid 2000s 2005 the standard was extended to 802.16E and this was known as mobile YMAX where mobility was added as another component of YMAX. And as I have already pointed out the YMAX basically is based on OFDM or Orthogonal Frequency Division Multiplexing which is sort of an advanced signal transmission technique and significantly enhances the signal strength and the data rate to achieve broadband communication capabilities. And therefore it is widely recognized as the choicest strategy for transmission of signals in broadband wireless access for instance be it wireless LAN or LTE which is another 4G wireless standard or Bluetooth and so on. And this is a table which shows some of the specs or the key aspects of YMAX. Most of them are fairly advanced but what you can look at is basically the overall bandwidth if you look at the bandwidth this channel bandwidth it can support bandwidths all the way from 5, 10 to 20 mega or so supports a huge bandwidth which means simultaneously can support a huge data rate corresponding to these huge bandwidths. If you remember WCDMA has a bandwidth of about 5 megahertz YMAX can support a bandwidth of about 20 megahertz which means the data rate proportionately increases significantly. And YMAX again supports several advanced features such as adaptive modulation encoding that is that is adaptively changing the number of bits transmitted according to the strength of the link or the other aspects of the link so as to improve the efficiency very high peak data rates around 75 to 100 mega bits per second and advanced antenna techniques that is not just a single antenna but multiple antennas to significantly improve the received signal strength. These are different features which are summarized here. These are the space time codes which again increase the reliability through coding beam forming which basically focus the energy transmitted from the antennas in a particular direction to improve the energy efficiency of the antennas and therefore to increase the data rate or the signal strength to particular users and thereby improving the service. Spatial multiplexing which is transmitting which multiplexing more than one streams or more than one users therefore in space thereby transmitting either additional data to a single user or transmitting additional data to various users and this is an important feature which is made possible by multiple antennas and this is something that we are also going to see slightly supports also TDD and FDD that is time division duplex and frequency division duplex that is well uplink and downlink are either divided in different time slots or divided in different frequency band that gives additional flexibility for operation and also it enables what is known as dynamic resource allocation that is sharing the resources rather than GSM which has a fixed time slot for each user. Allows the resources to be shared dynamically thereby allocating more resources to data hungry users such as users who are on video calls or users who are on video streaming while allocating less users to users who are on applications or services that are not so data hungry such as voice calls which require less data rates. So this flexible scheduling is what helps or what enables efficiently handling several users or several types of users in this wireless network who are on different services such as video streaming, internet browsing, email browsing, file transfer, voice calling and so on that helps really address the challenge of handling this wide gamut of services very efficiently in this wireless mobile network and additionally resources can also be allocated using advanced antenna systems in the spatial domain that is because they are not limited to a single antenna but they can since they can support multiple antennas these users can be efficiently allocated or multiple users can be if multiple users and multiple data streams can be efficiently multiplexed using these advanced antenna systems. And what I have here is a basic Ymax frame structure which shows how the users can be the different users can be scheduled efficiently you as you can see these different blocks that are allocated for different applications or different users are asymmetric as you can see some of the blocks are very large some of the blocks are very small which means different users depending on the kind of application depending on the nature of the intensity of the data rate required by these different applications can be a propagated allocated resources thereby improving the overall efficiency and there are various services that are supported by Ymax such as voice which is known as the unsolicited grant service real-time polling service which is supported for applications such as video the non-real-time polling service for other applications such as FTP that is a basic file transfer best effort service for applications such as web browsing email internet etc and the extended real-time variable rate service or the ERT VR service also Ymax supports a variety of device mobility aspects for instance the device can be nobadic that is basically it's practically speaking not mobile except over except after an extended period of operation these can be devices such as for instance your desktop which is more or less installed at a particular place or a base station which is more or less fixed at a particular place after installation portable for instance devices which are mobile but devices which are not moving at a very high speed for instance a laptop which a user uses at a fixed position for a long duration such as a couple of hours before moving to another location etc simple mobility like mobile phones etc which users are in such as cars who are moving in speeds up to 60 kilometers per hour or less and full mobility for instance with devices such as other laptops or mobile phones with users in high speed mobile scenarios such as fast speed trains and can support mobility of up to about 120 kilometers per hour and the network architecture of Ymax is slightly different although it has a mobile station it has a base station these base stations are no longer connected on your conventional telephone lines to the other parts of the network the backhaul of what connects these base stations amongst themselves and to the other aspects are entirely based on an internet kind of type of network which is based on the transmission of data packets rather than which is known as a packet switched network so these are connected to the access service network gateways and these are connected through again an internet like network to a core service network which has several components such as gateways which connect to the other landline telephone network the 3G networks the 2G networks the internet and other IP networks and they also have modules for authentication mobile IP agents operational support systems business support systems such BSS such as billing ensuring or billing for the services etc and so on so the core network enables a vast set of rich set of services in this Ymax architecture in this Ymax cellular network so we will stop this introduction to the Ymax module here thank you very much