feat(bluetooth-classic): apply Kalman filter to RSSI values

Bluetooth Classic devices occasionally have some jumps in the measured
signal strengths, which this filter hopefully cleans up a bit. This
should lead to more consistent results, with less random "jumping".

src/integrations/bluetooth-classic/bluetooth-classic.service.spec.ts

@@ -13,10 +13,18 @@ import {
 } from './bluetooth-classic.const';
 import { NewRssiEvent } from './new-rssi.event';
 import { RoomPresenceDistanceSensor } from '../room-presence/room-presence-distance.sensor';
+import KalmanFilter from 'kalmanjs';
 
 jest.mock('child_process');
 jest.mock('util');
 jest.mock('../room-presence/room-presence-distance.sensor');
+jest.mock('kalmanjs', () => {
+  return jest.fn().mockImplementation(() => {
+    return {
+      filter: z => z
+    };
+  });
+});
 
 describe('BluetoothClassicService', () => {
   let service: BluetoothClassicService;
@@ -191,7 +199,7 @@ describe('BluetoothClassicService', () => {
       'test-instance',
       10
     );
-    expect(sensorInstance.timeout).toBe(30);
+    expect(sensorInstance.timeout).toBe(35);
   });
 
   it('should not distribute inquiries if not the leader', () => {
@@ -329,4 +337,33 @@ describe('BluetoothClassicService', () => {
     expect(nodes.find(node => node.id === 'def')).not.toBeUndefined();
     expect(nodes.find(node => node.id === 'xyz')).toBeUndefined();
   });
+
+  it('should filter the RSSI of inquired devices before publishing', async () => {
+    jest.spyOn(service, 'inquireRssi').mockResolvedValue(-3);
+    const handleRssiMock = jest
+      .spyOn(service, 'handleNewRssi')
+      .mockImplementation(() => undefined);
+    const filterRssiMock = jest
+      .spyOn(service, 'filterRssi')
+      .mockReturnValue(-5.2);
+
+    const address = 'ab:cd:01:23:00:70';
+    const expectedEvent = new NewRssiEvent('test-instance', address, -5.2);
+
+    await service.handleRssiRequest(address);
+    expect(filterRssiMock).toHaveBeenCalled();
+    expect(clusterService.publish).toHaveBeenCalledWith(
+      NEW_RSSI_CHANNEL,
+      expectedEvent
+    );
+    expect(handleRssiMock).toHaveBeenCalledWith(expectedEvent);
+  });
+
+  it('should reuse Kalman filters for the same address', () => {
+    service.filterRssi('D6:AB:CD:10:DA:31', -1);
+    service.filterRssi('D6:AB:CD:10:DA:41', -4);
+    service.filterRssi('D6:AB:CD:10:DA:31', -2);
+
+    expect(KalmanFilter).toHaveBeenCalledTimes(2);
+  });
 });

src/integrations/bluetooth-classic/bluetooth-classic.service.ts

@@ -22,11 +22,16 @@ import {
   REQUEST_RSSI_CHANNEL
 } from './bluetooth-classic.const';
 import { RoomPresenceDistanceSensor } from '../room-presence/room-presence-distance.sensor';
+import KalmanFilter from 'kalmanjs';
 
 @Injectable()
 export class BluetoothClassicService
   implements OnModuleInit, OnApplicationBootstrap {
   private readonly config: BluetoothClassicConfig;
+  private filterMap: Map<string, KalmanFilter> = new Map<
+    string,
+    KalmanFilter
+  >();
   private rotationOffset: number = 0;
   private logger: Logger;
 
@@ -73,9 +78,10 @@ export class BluetoothClassicService
    * @param address - Bluetooth MAC address
    */
   async handleRssiRequest(address: string): Promise<void> {
-    const rssi = await this.inquireRssi(address);
+    let rssi = await this.inquireRssi(address);
 
     if (rssi !== undefined) {
+      rssi = _.round(this.filterRssi(address, rssi), 1);
       const event = new NewRssiEvent(
         this.configService.get('global').instanceName,
         address,
@@ -166,6 +172,23 @@ export class BluetoothClassicService
     return matches?.length > 0 ? parseInt(matches[0], 10) : undefined;
   }
 
+  /**
+   * Applies the Kalman filter based on the historic values with the same address.
+   *
+   * @param address - Bluetooth MAC address
+   * @param rssi - Signal strength measurement for the given address
+   * @returns Smoothed signal strength value
+   */
+  filterRssi(address: string, rssi: number): number {
+    if (this.filterMap.has(address)) {
+      return this.filterMap.get(address).filter(rssi);
+    } else {
+      const kalman = new KalmanFilter({ R: 1.4, Q: 0.4 });
+      this.filterMap.set(address, kalman);
+      return kalman.filter(rssi);
+    }
+  }
+
   /**
    * Queries for the name of a Bluetooth device using the hcitool shell command.
    *
@@ -241,7 +264,7 @@ export class BluetoothClassicService
   protected calculateCurrentTimeout(): number {
     const nodes = this.getParticipatingNodes();
     const addresses = Object.values(this.config.addresses); // workaround for node-config deserializing to an Array-like object
-    return (Math.max(nodes.length, addresses.length) + 1) * 10;
+    return (Math.max(nodes.length, addresses.length) + 1.5) * 10;
   }
 
   /**