# Backscatter Communications: Inception of the Battery-Free Era--A Comprehensive Survey
## 4 BackCom: Signal Processing and Detection
### Signal Detection in BackCom
#### 4.2.2 Non-Coherent Detection
\begin{table}
\begin{tabular}{p{56.9 pt} p{142.3 pt} p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline \hline
**References** & **Scheme** & **Technique** & **Purpose** \\ \hline \hline \multicolumn{5}{c}{**Signal Processing**} \\ \hline \hline
[32] & Microcode. & Coding for Amb-BackCom, supports concurrent transmissions. & Achieve long ranges. \\ \hline
[66] & Cyclic codes. & Short cyclic error correcting codes for a BiS network. & Improve rate of transmissions. \\ \hline
[72] & Phase-based coding. & Coding based on 3 states of backscattered signal: negative phase, positive phase, and no backscatter signal for AmB-BackCom. & Improve throughput. \\ \hline
[73] & Channel codes. & Short block length channel codes for BiS. & Improve coverage. \\ \hline
[74] & Coupled coding and modulation. & Coupled usage of coding and modulation for BackCom. & Improve data rate. \\ \hline
[59] & Buzz. & Ideal for all backscatter tags as a virtual node. tags. & Reduce collisions among tags. \\ \hline
[77] & Full-duplex model. & Proposed full-duplex BackCom network design. & Deal with interference problems. \\ \hline
[78] & Several techniques. & Using the in-band full-duplex technique. & Reduce self-interference. \\ \hline
[82] & Anti-collisions. & Feasibility of anti-collision performance in a high density network. & Decrease collisions. \\ \hline
[32] & Multi-antenna decoding. & Channel estimation is not required for decoding. & Achieve decoding. \\ \hline
[73] & Decoding rule. & A composite hypothesis-testing decoding rule was designed. & Achieve a decoding standard. \\ \hline
[83] & BiGroup decoding. & Advantage of parallel decoding. & Feature fast decoding. \\ \hline  & \multicolumn{5}{c}{**Signal Detection**} \\ \hline
[65] & Designed an algorithm. & Formulated a transmission model. & Derive detection thresholds. \\ \hline
[66] & Bistatic coherent uncoded reception. & A coherent receiver for BiS radio was proposed. & Make detection simpler in BiS with an improved BER. \\ \hline
[67] & Up-link detection. & Designed theoretical models for two detectors in Amb-BackCom. & Derive thresholds for both detectors focused on the uplink detection problem. \\ \hline
[72] & Three-state detection scheme. & Detect between three states, i.e., positive phase, negative phase, and no-backscattering. & Improve data rate and the detectors for three states. \\ \hline
[73] & Non-coherent scheme. & Incorporates non-coherent channel coding with a BiS radio framework. & Less complexity than maximum likelihood (ML) detector. \\ \hline
[84] & Non-coherent scheme. & Joint probability distribution function of received signals was utilized for a non-coherent Amb-BackCom system. & Have a maximum likelihood detector. \\ \hline
[86] & Data detection approach. & A theoretical system model was formulated. & Achieve data detection with channel state information. \\ \hline
[89] & Cooperative receiver. & Signals can be recovered from an Amb-BackCom device and from RF sources. & Detect signals in a cooperative receiver. \\ \hline
[90] & Sub-optimal detector design. & Signal detection problem with differential modulation for Amb-BackCom. & Provide an approximate threshold for detection. \\ \hline
[91] & Multi-antenna reader scenario. & Transmission model for Amb-BackCom was proposed, where channel state information is unknown. & Provide different methods of detection. \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of signal processing and signal detection.