 Now we are going to look at some other interesting aspects of spectral efficiency These are not limited to 4g, but since our focus is the mobile broadband in the context of next-generation networks So we'd look at it from 4g perspective, but it is otherwise a Hot topic in communications so we'd look at the 4g requirements for spectral efficiency and then we'd look at some smart approaches which try to achieve such efficiency in 4g or LTE long-term evolution advanced the minimum requirements for peak spectral efficiency for 4g actually boils down to 15 bits per second per hertz in a single cell at the downlink and 6.75 in the uplink It is a very large number This is achieved through simultaneous utilization of the smart modulation techniques and usage of MIMO So it uses four by four antennas in the downlink. It means the base station Can support up to four simultaneous transmissions and four simultaneous receptions whereas on the mobile station, it supports two by four MIMO it means two simultaneous transmissions and support up to four possible receptions so 4g achieves more spectrum utilization by widening the spectrum So more bandwidth is provided for 4g network deployment The international mobile telecommunication advanced specification requires that up to 40 megahertz Scalable bandwidth has to be provided Now just compare this to the 5 megahertz requirement for 3g and mere 200 kilohertz requirement for 2g It means that 4g networks actually necessitate that more spectrum is allocated for these networks While providing such high spectral efficiency, there are certain Issues and certain areas which need to be taken care of for instance Assume there are certain cells Somehow, they are using same frequency This would cause interference at the periphery of these two cells If there is a Certain at certain point in time a signal which is on the edge of the cell Now it will actually have the lowest power Coming in from both these cells So it means it is expected to cause degradation in quality so it means when There are scenarios like this in which the periphery or the edge Areas are to be taken care of then the overall expectation of the spectral efficiency has to be reduced The recommendation is that the spectral efficiency of the periphery or the edge has to be 30 times less or more Around 30 times to the spectral efficiency that is provided to the users which are in close proximity To both these cells in their respective towers range