3.8 Channel Capacity

Channel capacities of in-house coaxial cable wiring can be calculated based on coaxial cable channel model, ingress noise model, and the transmit signal PSD. We use the following expression:

Equation 3.13

graphics/03equ13.gif

where we choose f ₁ = 42 MHz and f ₂ = 52 MHz. Channel capacities are shown in Figure 3.13 for PSD levels from 0 to 50 dBµV.

Figure 3.13. Channel Capacities of In-House Coaxial Cable Wiring

graphics/03fig13.gif

At a minimal transmit signal level of 0 dBµV, the channel capacity of the in-house coaxial cable wiring is small in the frequency band between 42 and 52 MHz. This is because the signal level is close to the noise floor of about -40 dBµV when the channel loss is about -30 dBµV. The effect of additional noise interference carriers further reduces the channel capacity. On the other hand, when the transmit signal level is relatively strong at 50 dBµV, about 316 millivolts (mV) on an impedance of 75 ohms, the channel capacity becomes about 60 Mbps. Under this transmit signal level, a home network transmission system with reasonable complexity of signal processing can be implemented for a transmission throughput of higher than 30 Mbps in the frequency gap of between 42 and 52 MHz.

3.9 MATLAB Files

3.9.1 Coaxial Cable Insertion Loss and Impulse Response Models

function [ht,h]=abcd2hcx(a,b,c,d);
d=a;
r=75;
sz=length(a);
h=2*r*ones(sz,1)./(r*(r*c+d)+(r*a+b));
h(sz+1:2*(sz-1))=real(h(sz-1:-1:2))-sqrt(-1)*imag(h(sz-1:-1:2));
ht=real(ifft(h));

3.9.2 Splitter Input-to-Output Model

function [a,b,c,d]=splitio(f,z0);
l1=4e-5;
l2=1e-7;
k1=0.9997;
k2=0.9997;
a=0.707;
r=220;
C=4.5e-12;
lf=length(f);
W=2*pi*f';
a10=ones(lf,1)/a/k1;
b10=j*W*l1*a*(1-k1^2)/k1;
c10=ones(lf,1)./(j*W*l1*a*k1);
d10=ones(lf,1)*a/k1;
a3=ones(lf,1);
b3=zeros(lf,1);
c3=j*C*W;
d3=a3;
a1=a10.*a3+b10.*c3;
b1=a10.*b3+b10.*d3;
c1=c10.*a3+d10.*c3;
d1=c10.*b3+d10.*d3;
a2=j*W*l2*(2*(1+k2)*z0+r)+r*z0-(1-k2^2)*W.^2*l2^2;
b2=j*W*l2*r*z0-(1-k2^2)*W.^2*l2^2*(r+z0);
c2=2*j*W*l2*(1+k2)+r;
d2=2*j*W*l2*(1+k2)*(r+z0)+r*z0;
a=a1.*a2+b1.*c2;
b=a1.*b2+b1.*d2;
c=c1.*a2+d1.*c2;
d=c1.*b2+d1.*d2;
delt=j*W*l2*(1+k2)*(r+2*z0)+r*z0;
a=a./delt;
b=b./delt;
c=c./delt;
d=d./delt;

3.9.3 Splitter Output-to-Output Model

function [a,b,c,d]=splitoo(f,z1);
l1=4e-5;
l2=1e-7;
k1=0.9997;
k2=0.9997;
a=0.707;
r=220;
C=4.5e-12;
lf=length(f);
W=2*pi*f';
zm=a^2*z1;
a1=zm+j*W*l2;
b1=j*W*l2*(1+k2).*(j*W*l2*(1-k2)+2*zm);
c1=ones(lf,1);
d1=zm+j*W*l2;
a=b1+a1*r;
b=r*b1;
c=C*(r+b1)-(1-a1).^2;
d=b1+a1*r;
delt=r+b1;
a=a./delt;
b=b./delt;
c=c./delt;
d=d./delt;

3.9.4 Coaxial Cable Wiring Channel Model

f=[1:1025]/1025*1.5e8;
l1=100;
l2=25;
l3=35;
z0=75;
z1=75;
load c6.mod
load c59.mod
[a1,b1,c1,d1]=abcdcx(f,c6(:,1),c6(:,2),c6(:,3),c6(:,4),c6(:,5),l1);
[a2,b2,c2,d2]=abcdcx(f,c6(:,1),c6(:,2),c6(:,3),c6(:,4),c6(:,5),l2);
[a3,b3,c3,d3]=abcdcx(f,c6(:,1),c6(:,2),c6(:,3),c6(:,4),c6(:,5),l3);
[as1,bs1,cs1,ds1]=splitoo(f,z1);
[as2,bs2,cs2,ds2]=splitio(f,z0);
[chip1,h1]=abcd2hcx(a1,b1,c1,d1);
y1=20*log10(abs(h1(1:1025)));
at1=a1.*as1+b1.*cs1;
bt1=a1.*bs1+b1.*ds1;
ct1=c1.*as1+d1.*cs1;
dt1=c1.*bs1+d1.*ds1;
[chip2,h2]=abcd2hcx(at1,bt1,ct1,dt1);
y2=20*log10(abs(h2(1:1025)));
at2=at1.*a2+bt1.*c2;
bt2=at1.*b2+bt1.*d2;
ct2=ct1.*a2+dt1.*c2;
dt2=ct1.*b2+dt1.*d2;
[chip3,h3]=abcd2hcx(at2,bt2,ct2,dt2);
y3=20*log10(abs(h3(1:1025)));
at3=at2.*as2+bt2.*cs2;
bt3=at2.*bs2+bt2.*ds2;
ct3=ct2.*as2+dt2.*cs2;
dt3=ct2.*bs2+dt2.*ds2;
[chip4,h4]=abcd2hcx(at3,bt3,ct3,dt3);
y4=20*log10(abs(h4(1:1025)));
a=at3.*a3+bt3.*c3;
b=at3.*b3+bt3.*d3;
c=ct3.*a3+dt3.*c3;
d=ct3.*b3+dt3.*d3;
[chip,h]=abcd2hcx(a,b,c,d);
y5=20*log10(abs(h(1:1025)));
figure(2)
plot(f,y1,'k',f,y5,'k')
figure(3)
plot([1:1025]/2/1.5e8,chip(1:1025),'k')

3.9.5 Ingress Noise Model

psize=2049;
nsub=500;
perc=0.5;
f=[0:psize-1]/2048*50e6;
f(1)=0.00001;
%define shortwave radio bands
mask1l=5.5e6;
mask1h=6e6;
mask2l=7e6;
mask2h=7.5e6;
mask3l=9e6;
mask3h=9.8e6;
mask4l=11.5e6;
mask4h=12e6;
mask5l=13.5e6;
mask5h=14e6;
mask6l=14.8e6;
mask6h=15e6;
mask7l=17.5e6;
mask7h=18e6;
mask8l=21.5e6;
mask8h=21.8e6;
%define 30 random peaks
rloc1=rand(1,30)*50e6;
rloc2=rand(1,30)*50e6;
rloc3=rand(1,30)*50e6;
rloc4=rand(1,30)*50e6;
rloc5=rand(1,30)*50e6;
rloc6=rand(1,30)*50e6;
rloc7=rand(1,30)*50e6;
rloc8=rand(1,30)*50e6;
%noise floor
nsfllog=-40;
nsflflog=ones(1,psize)*nsfllog;
nsflf=10.^(nsflflog/10);
%radio background noise level, e-filed
efildlog=34.5-20;
efildflog=ones(1,psize)*efildlog;
epowflog=efildflog-44.5;
epowf=10.^(epowflog/10);
%radio interference noise level, random e-field
erfildflog=rand(1,psize)*45;
%spectrum mask
erfmask=ones(1,psize)*0.1;
for i=1:psize
if f(i)>mask1l & f(i)<mask1h
erfmask(i)=1;
end
if f(i)>mask2l & f(i)<mask2h
erfmask(i)=1;
end
if f(i)>mask3l & f(i)<mask3h
erfmask(i)=1;
end
if f(i)>mask4l & f(i)<mask4h
erfmask(i)=1;
end
if f(i)>mask5l & f(i)<mask5h
erfmask(i)=1;
end
if f(i)>mask6l & f(i)<mask6h
erfmask(i)=1;
end
if f(i)>mask7l & f(i)<mask7h
erfmask(i)=1;
end
if f(i)>mask8l & f(i)<mask8h
erfmask(i)=1;
end
for j=1:30
if f(i)>rloc1(j)-100e3 & f(i)<rloc1(j)+100e3
erfmask(i)=0.2;
end
if f(i)>rloc2(j)-100e3 & f(i)<rloc2(j)+100e3
erfmask(i)=0.3;
end
if f(i)>rloc3(j)-100e3 & f(i)<rloc3(j)+100e3
erfmask(i)=0.4;
end
if f(i)>rloc4(j)-100e3 & f(i)<rloc4(j)+100e3
erfmask(i)=0.5;
end
if f(i)>rloc5(j)-100e3 & f(i)<rloc5(j)+100e3
erfmask(i)=0.6;
end
if f(i)>rloc6(j)-100e3 & f(i)<rloc6(j)+100e3
erfmask(i)=0.7;
end
if f(i)>rloc7(j)-100e3 & f(i)<rloc7(j)+100e3
erfmask(i)=0.8;
end
if f(i)>rloc8(j)-100e3 & f(i)<rloc8(j)+100e3
erfmask(i)=0.9;
end
end
end
erfildflog=erfildflog.*erfmask;
%conversion at 10 MHz
erpowflog=erfildflog-44.5;
erpowf=10.^(erpowflog/10);
%sum of background and interference noise power
epowf=epowf+erpowf;
%field to power: propotional to the power of wavelength
epowf=epowf.*(10e6./f).^2;
epowft=perc*epowf+nsflf;
f(1)=0;
nfilt=fir2(900,f/max(f),sqrt(epowft));
[h,w]=freqz(nfilt,1,1024);
px=[1:1024]/1024*50e6;
py=20*log10(abs(h));
plot(px(102:1024),py(102:1024),'k');
grid
xlabel('Frequency (Hz)')
ylabel('Noise Level (dBµV)')

3.9.6 Channel Capacity Calculation

coaxmod;
h2=(abs(h(1:1024))).^2;
nmdl;
n2=(abs(h(1:1024))).^2;
df=max(f)/1025;
f1=ceil(1025*42e6/1.5e8);
f2=ceil(1025*52e6/1.5e8);
for psd=0:50
chacap(psd+1)=sum(log(1+10^(psd/10).*h2(f1:f2)./n2(f1:f2)))*df/log(2);
end
px=[0:50]
figure(3)
plot(px,chacap,'k');
grid
xlabel('Transmit Signal Level (dBµV)')
ylabel('Channel Capacity (Bits/Sec)')