👭 😯 🍒 软件无线电-它如何工作？第7部分 👹 🚱 🌨️

哈Ha

在关于向GNU Radio传输的上一部分中，询问了是否可以使用SDR解码LoRa协议（低功率设备的数据传输）的问题。这个主题对我来说似乎很有趣，特别是因为LoRa信号本身很不寻常-所谓的线性调频扩频调制或“线性调频调制”。

运作方式，继续削减。

顺便说一句，线性调频调制的字面翻译听起来像是“鸣叫调制”，但听起来完全是超现实的，所以我最好留下一个简单的词“线性调频”（如评论中所建议，俄语中称为线性频率调制）。

LoRa调制

如上所述，当发送LoRa时，通过Semtech的专利使用了使用“线性调频”的调制方法。如果有人想用公式来实现细节，您可以在semtech网站上或此处阅读PDF，但是如果非常不礼貌，那么一个“ chi”就是一个频率变化，并且比特流是用这种变化编码的，如上图所示。 LoRa中的信号参数是SF（扩频因子-实际上是一个“线性调频”的持续时间）和带宽-传输带宽。 SF参数由预定义的SF7值SF12设置，其中7是最快的模式，而12是最慢的模式（例如，您可以看到一张图片，上面显示了使用researchgate different声的不同速度）。

显然，“线性调频”的长度越短，频带越宽，则可以获得更快的传输速度。所有这些都是通过这样的表连接的：

从距离和抗干扰性的角度来看，缓慢而令人悲伤的传输是有利的，但首先，我们会失去速度，其次，我们会浪费时间，并且根据LoRa规则，该设备最多可以传输1％的时间，以免打扰他人设备。因此，为低功率设备选择最佳传输速度也不是一件容易的事。

希望我有一个基本原则，现在让我们继续进行SDR和解码。

铁

为了进行测试，我使用了LoRa Click RN2483和Arduino M0，只是因为它们可用。

这是用于原型制作的相当方便的尺寸，因为它使您可以轻松地将板子彼此替换而不用焊接（这种称为MikroBUS的格式有许多不同的外围设备可用）。

在伪造者下添加了不伪装成生产的草稿代码。值“ 1234”作为测试通过。

rn2483_tx.ino

// RN2483 Modem and LoRa Click test TX. Tested with Arduino M0 int reset = A2; int rts = 9; // CS int cts = 3; // INT // the setup routine runs once when you press reset: void setup() { Serial1.begin(57600); // Serial port to radio // output LED pin pinMode(LED_BUILTIN, OUTPUT); pinMode(cts, INPUT); pinMode(rts, OUTPUT); digitalWrite(rts, HIGH); // Reset rn2483 pinMode(reset, OUTPUT); digitalWrite(reset, LOW); delay(100); digitalWrite(reset, HIGH); delay(100); sendCommand("sys get ver\r\n"); sendCommand("sys get hweui\r\n"); sendCommand("mac pause\r\n"); sendCommand("radio set mod lora\r\n"); sendCommand("radio set pwr -3\r\n"); // the transceiver output power, from -3 to 15 sendCommand("radio set sf sf8\r\n"); // sf7..sf12, sf7 the fastest spreading factor but gives the shortest range // sendCommand("mac set dr 0\r\n"); // data rate: 0-4, 4 faster sendCommand("radio set freq 869100000\r\n"); // sendCommand("radio set afcbw 41.7\r\n"); sendCommand("radio set rxbw 125\r\n"); // sendCommand("radio set prlen 8\r\n"); sendCommand("radio set crc on\r\n"); // sendCommand("radio set iqi off\r\n"); sendCommand("radio set cr 4/8\r\n"); // sendCommand("radio set wdt 60000\r\n"); // disable for continuous reception // sendCommand("radio set sync 12\r\n"); sendCommand("radio set bw 125\r\n"); } void sendCommand(const char *cmd) { Serial1.print(cmd); String incoming = Serial1.readString(); // SerialUSB.print(cmd); // SerialUSB.println(incoming); } // the loop routine runs over and over again forever: void loop() { char data[64] = {0}; // hexadecimal value representing the data to be transmitted, from 0 to 255 bytes for LoRa modulation and from 0 to 64 bytes for FSK modulation. sprintf(data, "radio tx 1234\r\n"); sendCommand(data); if (msg_num > 10000) msg_num=0; digitalWrite(LED_BUILTIN, 1); delay(400); digitalWrite(LED_BUILTIN, 0); delay(600); }

顺便说一句，RN2483的最大声明传输距离可达15 km，实际上，在有一层建筑物的情况下，该信号已经消失1 km，并且在城市“蚁丘”中不能超过100 m。

我们启动调制解调器，然后继续解码。

解码方式

GNU Radio本身不提供LoRa支持，因此您必须使用第三方组件。他们只有两个，不幸的是，两位作者的名字都没有显示出任何想象力，他们称呼它们完全一样-gr-lora（ https://github.com/rpp0/gr-lora和https://github.com/ BastilleResearch / gr-lora ）。不幸的是，由于GNU Radio不能同时拥有两个组件，因此一个组件的安装程序会覆盖另一个组件的文件。

rpp0 / gr-lora

您可以从github下载解码器源，该程序集是标准的，不会造成困难：

 git clone https://github.com/rpp0/gr-lora.git cd gr-lora mkdir build cd build cmake .. make && sudo make install && sudo ldconfig

安装后，其他块会出现在GNU Radio中，很容易从中组装解码器。作为解码器的参数，必须指定传输带宽，扩频因子，SDR的中心频率和接收频率。

GNU Radio中的单元是标准化的，因此可以使用任何接收器，例如RTL-SDR。我使用了SDRPlay。使用一个简单的Python程序将数据输出到控制台。

udp_receive.py

 import socket UDP_IP = "127.0.0.1" UDP_PORT = 40868 sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) # UDP sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) sock.bind((UDP_IP, UDP_PORT)) sock.settimeout(0.5) while True: try: data, addr = sock.recvfrom(128) # buffer size is 1024 bytes print("Msg:", ' '.join('{:02x}'.format(x) for x in data)) except socket.timeout: pass

工作结果如图所示。

如您所见，该行包含传输的标题和结尾块，在中间，我们看到了数据“ 1234”。

巴士底狱研究/ gr-lora

该模块值得注意，因为它不仅可以在接收时工作，而且可以在传输时工作。安装大致相同：需要从源头组装组件。

 git clone git://github.com/BastilleResearch/gr-lora.git cd gr-lora mkdir build cd build cmake .. make && sudo make install && sudo ldconfig

该解码器的连接图如图所示。

如您所见，还有更多的街区。旋转器和多相重采样器选择所需的频率并切断多余的频率，解调器将“线性调频”转换为二进制代码（输出为“ 17 00 3e 00 38 00 2f 00 01 00 39 00 2c 00 30 00 c6 00 18 00 7e 00 d5 00 85 00 e9 00 d8 00 67 00 c4 00”），然后解码器形成最终包。

不幸的是，它永远无法正常工作。解码肯定有效，而调制解调器正在工作时，数据会出现，但是接收到的消息与传输的消息无关。

我不明白原因，可能是我在某处的设置中犯了一个错误，或者此解码器仅与我自己的编码器兼容。那些希望的人可以使用渠道模型独立检查。

广域网

如您所见，此处考虑了较低的物理传输层。在更高级别的LoRaWAN协议中，另一个逻辑层位于顶层-具有加密，密钥和其他服务。那些想了解编码方式的人可以在这里尝试在线解码器。

顺便说一句，即使我们使用SDR接收到LoRaWAN信号，而没有加密密钥（其中一个存储在提供商的服务器上），我们仍然无法识别数据包的内容。

结论

如您所见，使用SDR解码LoRa是很有可能的。当然，基于SDR创建真实的网关几乎是不可取的-它的灵敏度将比专门设计用于接收微弱信号并且具有更多窄带滤波器和LNA的“真实”调制解调器的灵敏度差。但是对于测试或研究，这可能会很有趣。

对于那些想要自己尝试的人，GNU Radio源grc文件位于破坏者之下。

receive1.grc

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<sink_key>0</sink_key> </connection> <connection> <source_block_id>sdrplay_rsp2_source_0</source_block_id> <sink_block_id>blocks_rotator_cc_0</sink_block_id> <source_key>0</source_key> <sink_key>0</sink_key> </connection> </flow_graph>

receive2.grc

 <?xml version='1.0' encoding='utf-8'?> <?grc format='1' created='3.7.11'?> <flow_graph> <timestamp>Mon Jun 3 09:39:45 2019</timestamp> <block> <key>options</key> <param> <key>author</key> <value></value> </param> <param> <key>window_size</key> <value></value> </param> <param> <key>category</key> <value>[GRC Hier Blocks]</value> </param> <param> <key>comment</key> <value></value> </param> <param> <key>description</key> <value></value> </param> <param> <key>_enabled</key> <value>True</value> </param> <param> <key>_coordinate</key> <value>(8, 8)</value> </param> <param> <key>_rotation</key> <value>0</value> </param> <param> <key>generate_options</key> <value>wx_gui</value> </param> <param> <key>hier_block_src_path</key> <value>.:</value> </param> <param> <key>id</key> <value>top_block</value> </param> <param> <key>max_nouts</key> <value>0</value> </param> <param> <key>qt_qss_theme</key> <value></value> </param> <param> <key>realtime_scheduling</key> <value></value> </param> <param> <key>run_command</key> <value>{python} -u {filename}</value> </param> <param> <key>run_options</key> <value>prompt</value> </param> <param> <key>run</key> <value>True</value> </param> <param> <key>thread_safe_setters</key> <value></value> </param> <param> <key>title</key> <value></value> </param> </block> <block> <key>variable</key> <param> <key>comment</key> <value></value> </param> <param> <key>_enabled</key> <value>True</value> </param> <param> <key>_coordinate</key> <value>(184, 12)</value> </param> <param> <key>_rotation</key> <value>0</value> </param> <param> <key>id</key> <value>samp_rate</value> </param> <param> <key>value</key> <value>1000000</value> </param> </block> <block> <key>lora_lora_receiver</key> <param> <key>bandwidth</key> <value>125000</value> </param> <param> <key>alias</key> <value></value> </param> <param> <key>crc</key> <value>True</value> </param> <param> <key>center_freq</key> <value>869e6</value> </param> <param> <key>channel_list</key> <value>[869.1e6]</value> </param> <param> <key>cr</key> <value>4</value> </param> <param> <key>comment</key> <value></value> </param> <param> <key>conj</key> <value>False</value> </param> <param> <key>affinity</key> <value></value> </param> <param> <key>decimation</key> <value>1</value> </param> <param> <key>disable_channelization</key> <value>False</value> </param> <param> <key>disable_drift_correction</key> <value>False</value> </param> <param> <key>_enabled</key> <value>True</value> </param> <param> <key>_coordinate</key> <value>(456, 332)</value> </param> <param> <key>_rotation</key> <value>0</value> </param> <param> <key>id</key> <value>lora_lora_receiver_0</value> </param> <param> <key>implicit</key> <value>False</value> </param> <param> <key>maxoutbuf</key> <value>0</value> </param> <param> <key>minoutbuf</key> <value>0</value> </param> <param> <key>reduced_rate</key> <value>False</value> </param> <param> <key>samp_rate</key> <value>1e6</value> </param> <param> <key>sf</key> <value>8</value> </param> </block> <block> <key>lora_message_socket_sink</key> <param> <key>alias</key> <value></value> </param> <param> <key>comment</key> <value></value> </param> <param> <key>affinity</key> <value></value> </param> <param> <key>_enabled</key> <value>True</value> </param> <param> <key>_coordinate</key> <value>(696, 364)</value> </param> <param> <key>_rotation</key> <value>0</value> </param> <param> <key>id</key> <value>lora_message_socket_sink_0</value> </param> <param> <key>ip</key> <value>127.0.0.1</value> </param> <param> <key>layer</key> <value>1</value> </param> <param> <key>port</key> <value>40868</value> </param> </block> <block> <key>sdrplay_rsp2_source</key> <param> <key>agc_enabled</key> <value>False</value> </param> <param> <key>antenna</key> <value>'A'</value> </param> <param> <key>bw</key> <value>400</value> </param> <param> <key>alias</key> <value></value> </param> <param> <key>comment</key> <value></value> </param> <param> <key>affinity</key> <value></value> </param> <param> <key>dc_offset_mode</key> <value>True</value> </param> <param> <key>debug_enabled</key> <value>False</value> </param> <param> <key>device_serial</key> <value>'0'</value> </param> <param> <key>_enabled</key> <value>True</value> </param> <param> <key>_coordinate</key> <value>(72, 148)</value> </param> <param> <key>_rotation</key> <value>0</value> </param> <param> <key>id</key> <value>sdrplay_rsp2_source_0</value> </param> <param> <key>if_atten_db</key> <value>30</value> </param> <param> <key>ifType</key> <value>0</value> </param> <param> <key>iq_balance_mode</key> <value>True</value> </param> <param> <key>lna_atten_step</key> <value>3</value> </param> <param> <key>lo_mode</key> <value>1</value> </param> <param> <key>maxoutbuf</key> <value>0</value> </param> <param> <key>minoutbuf</key> <value>0</value> </param> <param> <key>rf_freq</key> <value>869.0e6</value> </param> <param> <key>sample_rate</key> <value>samp_rate</value> </param> </block> <block> <key>wxgui_fftsink2</key> <param> <key>avg_alpha</key> <value>0</value> </param> <param> <key>average</key> <value>True</value> </param> <param> <key>baseband_freq</key> <value>0</value> </param> <param> <key>alias</key> <value></value> </param> <param> <key>comment</key> <value></value> </param> <param> <key>affinity</key> <value></value> </param> <param> <key>_enabled</key> <value>True</value> </param> <param> <key>fft_size</key> <value>1024</value> </param> <param> <key>freqvar</key> <value>None</value> </param> <param> <key>_coordinate</key> <value>(688, 108)</value> </param> <param> <key>_rotation</key> <value>0</value> </param> <param> <key>grid_pos</key> <value></value> </param> <param> <key>id</key> <value>wxgui_fftsink2_0</value> </param> <param> <key>notebook</key> <value></value> </param> <param> <key>peak_hold</key> <value>True</value> </param> <param> <key>ref_level</key> <value>0</value> </param> <param> <key>ref_scale</key> <value>2.0</value> </param> <param> <key>fft_rate</key> <value>15</value> </param> <param> <key>samp_rate</key> <value>samp_rate</value> </param> <param> <key>title</key> <value>FFT Plot</value> </param> <param> <key>type</key> <value>complex</value> </param> <param> <key>win_size</key> <value></value> </param> <param> <key>win</key> <value>None</value> </param> <param> <key>y_divs</key> <value>10</value> </param> <param> <key>y_per_div</key> <value>10</value> </param> </block> <connection> <source_block_id>lora_lora_receiver_0</source_block_id> <sink_block_id>lora_message_socket_sink_0</sink_block_id> <source_key>frames</source_key> <sink_key>in</sink_key> </connection> <connection> <source_block_id>sdrplay_rsp2_source_0</source_block_id> <sink_block_id>lora_lora_receiver_0</sink_block_id> <source_key>0</source_key> <sink_key>0</sink_key> </connection> <connection> <source_block_id>sdrplay_rsp2_source_0</source_block_id> <sink_block_id>wxgui_fftsink2_0</sink_block_id> <source_key>0</source_key> <sink_key>0</sink_key> </connection> </flow_graph>

所有成功的实验。

软件无线电-它如何工作？ 第7部分

LoRa调制

铁

解码方式

广域网

结论

More articles:

软件无线电-它如何工作？第7部分