public RealAntennaDigital(RealAntenna orig) : base(orig)
{
if (orig is RealAntennaDigital o)
{
modulator = new RAModulator(o.modulator);
}
}
// Voyager ~= 14 bits (115,200 down to 10 bps)
// NEAR: 5 bits (1.1kbps - 26.5kbps)
// MRO: Symbol rates (80 - 6000000 s/s) 16 bits although it actually is lots of different ranges for different encoders.
// JUNO: Symbol rates 23 - 1.2M ~= 16 bits
// Given Bandwidth, DataRate and SpectralEfficiency, compute minimum C/I from Shannon-Hartley.
// C = B log_2 (1 + SNR), where C=Channel Capacity and SNR is linear. 10*Log10(SNR) to convert to dB.
// We will substitute C = (DateRate / SpectralEfficiency) to account for non-ideal performance
// Actually, let's just skip to digital land, let the Encoder specify required Eb/N0, and derive
// Derive: Es/N0 as Eb/N0 + 3*bits
// bandwidth as a function of the symbol rate and the spectral efficiency.
public virtual bool Compatible(RAModulator other)
{
if (MinSymbolRate > other.SymbolRate)
{
return(false);
}
if (other.MinSymbolRate > SymbolRate)
{
return(false);
}
return(true);
}
private bool BestPeerModulator(RealAntenna rx, out double modRate, out double codeRate)
{
RealAntennaDigital tx = this;
Antenna.Encoder encoder = Antenna.Encoder.BestMatching(tx.Encoder, rx.Encoder);
codeRate = encoder.CodingRate;
modRate = 0;
if (!(rx is RealAntennaDigital))
{
return(false);
}
if (!Compatible(rx))
{
return(false);
}
if ((tx.Parent is ModuleRealAntenna) && !tx.Parent.CanComm())
{
return(false);
}
if ((rx.Parent is ModuleRealAntenna) && !rx.Parent.CanComm())
{
return(false);
}
Vector3 toSource = rx.Position - tx.Position;
double distance = toSource.magnitude;
RAModulator txMod = tx.modulator, rxMod = (rx as RealAntennaDigital).modulator;
if ((distance < tx.MinimumDistance) || (distance < rx.MinimumDistance))
{
return(false);
}
if (!txMod.Compatible(rxMod))
{
return(false);
}
int maxBits = Math.Min(txMod.ModulationBits, rxMod.ModulationBits);
double maxSymbolRate = Math.Min(txMod.SymbolRate, rxMod.SymbolRate);
double minSymbolRate = Math.Max(txMod.MinSymbolRate, rxMod.MinSymbolRate);
double RxPower = Physics.ReceivedPower(tx, rx, distance, tx.Frequency);
double temp = Physics.NoiseTemperature(rx, tx.Position);
double N0 = Physics.NoiseSpectralDensity(temp); // In dBm
double minEb = encoder.RequiredEbN0 + N0; // in dBm
double maxBitRateLog = RxPower - minEb; // in dB*Hz
double maxBitRate = RATools.LinearScale(maxBitRateLog);
/*
* Vessel tv = (tx.ParentNode as RACommNode).ParentVessel;
* Vessel rv = (rx.ParentNode as RACommNode).ParentVessel;
* if (tv != null && rv != null)
* {
* string debugStr = $"{ModTag} {tx} to {rx} RxP {RxPower:F2} vs temp {temp:F2}. NSD {N0:F1}, ReqEb/N0 {encoder.RequiredEbN0:F1} -> minEb {minEb:F1} gives maxRate {RATools.PrettyPrint(maxBitRate)}bps vs symbol rates {RATools.PrettyPrint(minSymbolRate)}Sps-{RATools.PrettyPrint(maxSymbolRate)}Sps";
* Debug.Log(debugStr);
* }
*/
// We cannot slow our modulation enough to achieve the required Eb/N0, so fail.
if (maxBitRate < minSymbolRate)
{
return(false);
}
double targetRate;
int negotiatedBits;
if (maxBitRate <= maxSymbolRate)
{
// The required Eb/N0 occurs at a lower symbol rate than we are capable of at 1 bit/sec/Hz.
// Step down the symbol rate and modulate at 1 bit/sec/Hz (BPSK).
// (What if the modulator only supports schemes with >1 bits/symbol?)
// (Then our minimum EbN0 is an underestimate.)
float ratio = Convert.ToSingle(maxBitRate / maxSymbolRate);
double log2 = Math.Floor(Mathf.Log(ratio, 2));
targetRate = maxSymbolRate * Math.Pow(2, log2);
negotiatedBits = 1;
//debugStr += $" Selected rate {RATools.PrettyPrint(targetRate)}bps (MaxSymbolRate * log2 {log2})";
}
else
{
// We need to go to SNR here and rely a bit more on Shannon-Hartley
double Noise = N0 + RATools.LogScale(maxSymbolRate);
double CI = RxPower - Noise;
double margin = CI - encoder.RequiredEbN0;
targetRate = maxSymbolRate;
negotiatedBits = Math.Min(maxBits, Convert.ToInt32(1 + Math.Floor(margin / 3)));
//debugStr += $" Noise {Noise:F2} CI {CI:F2} margin {margin:F1}";
}
modRate = targetRate * negotiatedBits;
//Debug.LogFormat(debugStr);
return(true);
// Energy/bit (Eb) = Received Power / datarate
// N0 = Noise Spectral Density = K*T
// Noise = N0 * BW
// SNR = RxPower / Noise = RxPower / (N0 * BW) = Eb*datarate / N0*BW = (Eb/N0) * (datarate/BW)
// I < B * log(1 + S/N) where I = information rate, B=Bandwidth, S=Total Power, N=Total Noise Power = N0*B
//
// Es/N0 = (Total Power / Symbol Rate) / N0
// = Eb/N0 * log(modulation order)
}
public RealAntennaDigital(string name) : base(name)
{
modulator = new RAModulator(this);
}
public void Copy(RAModulator orig)
{
ModulationBits = orig.ModulationBits;
}
public RAModulator(RAModulator orig) : this(orig.Parent, orig.ModulationBits)
{
}
public void Copy(RAModulator orig)
{
SymbolRate = orig.SymbolRate;
ModulationBits = orig.ModulationBits;
TechLevel = orig.TechLevel;
}
public RAModulator(RAModulator orig) : this(orig.SymbolRate, orig.ModulationBits, orig.TechLevel)
{
}