From cca0199d6377de5f2487ecf538286e82795f409b Mon Sep 17 00:00:00 2001
From: Ahmet Inan <xdsopl@gmail.com>
Date: Fri, 10 Feb 2023 11:24:18 +0100
Subject: [PATCH] omit guard between synchronization symbols

---
 decode.cc | 8 ++++----
 encode.cc | 9 +++++----
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/decode.cc b/decode.cc
index 69dd89c..470146e 100644
--- a/decode.cc
+++ b/decode.cc
@@ -85,8 +85,8 @@ public:
 	bool operator()(const cmplx *samples)
 	{
 		cmplx S = fsh();
-		cmplx P = conj(S) * cor(S * samples[search_pos] * conj(samples[search_pos+symbol_len+guard_len]));
-		value R = value(0.5) * pwr(norm(samples[search_pos]) + norm(samples[search_pos+symbol_len+guard_len]));
+		cmplx P = conj(S) * cor(S * samples[search_pos] * conj(samples[search_pos+symbol_len]));
+		value R = value(0.5) * pwr(norm(samples[search_pos]) + norm(samples[search_pos+symbol_len]));
 		value min_R = 0.0001 * symbol_len;
 		R = std::max(R, min_R);
 		value timing = match(norm(P) / (R * R));
@@ -115,11 +115,11 @@ public:
 		if (!process)
 			return false;
 
-		frac_cfo = phase_max / value(symbol_len+guard_len);
+		frac_cfo = phase_max / value(symbol_len);
 
 		DSP::Phasor<cmplx> osc;
 		osc.omega(frac_cfo);
-		symbol_pos = search_pos - index_max + guard_len;
+		symbol_pos = search_pos - index_max;
 		index_max = 0;
 		timing_max = 0;
 		for (int i = 0; i < symbol_len; ++i)
diff --git a/encode.cc b/encode.cc
index bef988e..f4fd0bd 100644
--- a/encode.cc
+++ b/encode.cc
@@ -48,7 +48,7 @@ struct Encoder
 	{
 		return 1 - 2 * bit;
 	}
-	void symbol()
+	void symbol(bool output_guard = true)
 	{
 		bwd(tdom, fdom);
 		for (int i = 0; i < symbol_len; ++i)
@@ -58,7 +58,8 @@ struct Encoder
 			x = value(0.5) * (value(1) - std::cos(DSP::Const<value>::Pi() * x));
 			guard[i] = DSP::lerp(guard[i], tdom[i+symbol_len-guard_len], x);
 		}
-		pcm->write(reinterpret_cast<value *>(guard), guard_len, 2);
+		if (output_guard)
+			pcm->write(reinterpret_cast<value *>(guard), guard_len, 2);
 		pcm->write(reinterpret_cast<value *>(tdom), symbol_len, 2);
 		for (int i = 0; i < guard_len; ++i)
 			guard[i] = tdom[i];
@@ -76,13 +77,13 @@ struct Encoder
 		for (int i = first_subcarrier; i < first_subcarrier + subcarrier_count; ++i)
 			fdom[i] = fdom[i+1];
 		fdom[first_subcarrier+subcarrier_count] = 0;
-		symbol();
+		symbol(false);
 #else
 		fdom[first_subcarrier] = std::sqrt(value(2 * symbol_len) / value(subcarrier_count));
 		for (int i = first_subcarrier + 1; i < first_subcarrier + subcarrier_count; ++i)
 			fdom[i] = fdom[i-1] * cmplx(nrz(seq()));
 		symbol();
-		symbol();
+		symbol(false);
 #endif
 	}
 	cmplx mod_map(code_type *b)