o To Simulate Cognitive Radio System which is so effective that it can harvest more band-width in highly desired bands than is currently in use! – More than in use by cellular systems – More than in use by unlicensed bands – More than in use by private mobile systems o This represents a paradigm shift in technology!

o Today’s radio systems are not aware of their radio spectrum environment and operate in a specific frequency band. o In some locations or some times of the day, 70 percent of the allocated spectrum may be sitting idle. o New bandwidth-intensive wireless services are being offered. o Unlicensed users constrained to a few overloaded bands o Increasing number of users. o This growth requires more spectral bandwidth to satisfy the demand.

o Intelligent radio that uses spectrum licensed to other users when they aren't using it. – ‘Bandwidth Harvesting’ o It is a software-designed radio with cognitive software. o CR can sense the environment. o CR adapts its way of communication to minimize the caused interference. o CR coexists with the primary user (using the same frequency band) in two ways: Concurrent and Opportunistic. Figure: A four-nodes wireless sensor network scenario.

o Full Cognitive Radios do not exist at the moment and are not likely to emerge until o Requires practical implementation of fully flexible SDR technologies and the intelligence required to exploit them cognitively. o But, true cognition and fully flexible radios may not be needed. o Simple intelligence and basic reconfigurability at the physical layer could provide significant benefits over traditional types of radio. o CR prototypes to emerge within the next five years. o Some devices are already in use like WLANs

o Dynamic Spectrum Access ( DSA ) o To fill the spectral holes with secondary users’ data.

Fc1 = 1000; Fc2 = 2000; Fc3 = 3000; Fc4 = 4000; Fc5 = 5000; Fs = 12000; x1 = cos(2*pi*1000*t); in_p = input('\nDo you want to enter first primary user Y/N: ','s'); if(in_p == 'Y' | in_p == 'y') y1 = ammod(x1,Fc1,Fs); end : in_p = input('Do you want to enter fifth primary user Y/N: ','s'); if(in_p == 'Y' | in_p == 'y') y5 = ammod(x1,Fc5,Fs); end y = y1 + y2 + y3 + y4 + y5; Pxx = periodogram(y); Hpsd = dspdata.psd(Pxx,'Fs',Fs); plot(Hpsd);

in_p = input('\nDo you want to enter a secondary user Y/N: ','s'); if(in_p == 'Y' | in_p == 'y') chek1 = Pxx(25)*10000; chek2 = Pxx(46)*10000; chek3 = Pxx(62)*10000; Code Portion Skipped : else disp('all user slots in use. try again later,'); end

inp_t=input('do u want to empty a slot: ','s'); if(inp_t=='Y'|inp_t=='y') inp_t=input('which slot do u want to empty for ur entry: ','s'); switch(inp_t) case ('1') y1=0; disp('slot1 is fired'); y = y1 + y2 + y3 + y4 + y5; case('2') y2=0; disp('slot2 is fired'); y = y1 + y2 + y3 + y4 + y5; : otherwise disp('invalid slot entered'); end

inp_t=input('do u want to add noise: ','s'); if(inp_t=='y'|inp_t=='Y') d = input('Enter the SNR in dB: '); figure Y = awgn(y,d); Pxx1 = periodogram(Y); Code Portion Skipped tm = 1-tem; Z = y.*tm; disp('attenuating'); grid on plot(Z);

Data assigned Allocated / Used Spectrum Band Un-allocated Bands / Spectrum Holes

Left over Spectral Gaps Spectral Gap Filled by modulating the new incoming user’s data over it

o Mobile multimedia downloads which require moderate data rates o Emergency communications services that require a moderate data rate and localized coverage (for example, video transmission from firemen’s’ helmets); o Broadband wireless networking (for example, using nomadic laptops), which needs high data rates, but where users may be satisfied with localized “hot spot” services; o Multimedia wireless networking services (e.g. audio/video distribution within homes) requiring high data rates.

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